《星际争霸》和象棋中确实存在滑坡效应，但撇开这个消极属性不提，这两者都是好游戏。在象棋中，玩家损失一个棋子，他的攻击能力、防御能力和控制能力都会稍逊一筹。当 然，象棋中还有其他许多因素——定位、势头、布阵等，决定着玩家到底是不是“失败”，当然损失一枚棋子也确实产生了一定的效应。显然，损失太多棋子，比如8个，玩家就彻 底处于劣势了。要赢回来简直是猴子捞月了。所谓的胜利，其实是“赢”了很多、很多步，最后来一个“致命一击”的累积效应。
说到游戏的经济系列方面，《星际争霸》的滑坡效应表现更为明显。假设对方提前进攻你，你hold住了。其他方面损失不相上下，但你还多损失了一个生产单位。放到其他游戏中 ，这大约就相当于落后一分。但在《星际争霸》里，后果就严重多了，因为采矿量的增长接近于指数型，你的对手在资源上只领先你一个生产单位，收益就比你翻了好几番。在你 损失那个生产单位起，你就已经在斜坡上往下滚了，此时的劣势效应正在无限放大。
格斗游戏中一般不存在滑坡效应。比如在《街霸》中，你的角色即使只剩一口气了，仍然行动自如。被打中只是让你的命值（得分）受损，但并不会限制你的行动选择，这点和象 棋中损失一个棋子或在《星际》中损失一个工作单位造成的恶果是不一样的。《武士之刃》中倒是意外地存在滑坡效应。在游戏中，被打中腿，玩家就会行走蹒跚；被打中手臂， 可能那手臂膊就算是残了。这在格斗游戏中是极为罕见的。
虽然，从现实一点的角度讲，快死的角色也是可能慢慢地爬着，至于能爬多远就另当别论了，但这样的游戏也太没意思了。（游戏邦注：至少在《武士之刃》中，这部分会持续数 秒钟，然后你才挂掉。）在《街霸》中，复原是很频繁的，所以所有玩家都能“笑到最后”。其实《街霸》中还是存在一点点滑坡效应的（如果你气数将近，你肯定很担忧被堵在 角落，而当你的血条全满时，你从来不担心这个），但总的来说，这是个中性的滑坡效应。
有一款格斗游戏因为是个例外而显得格外突出，它就是《Marvel vs. Capcom 2》。在这款游戏中，各名玩家选择3名角色。在任意给定的时间内，屏幕是只出显一名可活动的角色 ，其余二名则在屏幕之外的地方恢复受损的精力。玩家可以召唤屏幕之外的角色来辅助主角色，之后再切换屏幕。主角色可以与辅助角色一起发动攻击，从而丰富进攻策略和技巧 。玩家可以任意转换活动角色，但如果他已经损失了所有角色，就算是失败了。在这里，滑坡效应就出现了。当玩家只剩最后一个角色时，而其对方仍然有两个甚至全部角色无损 ，那么前者就明显处于下风。玩家的当前角色没有办法得到辅助攻击，胜算可谓微乎其微。恢复在这款游戏中相当少，游戏往往在玩家“技穷”以前就结束了。
带有“出圈即败”设计的格斗游戏，如《Virtua Fighter》和《Soul Calibur》就尤其不具有滑坡特征了。在这些游戏中，如果一名玩家的角色被推出圆圈，则玩家马上失败，无 论此时角色的血条还有多长。从根本上说，无论你目前落后对手多少、无论你的血条还有多少，出了圆圈对你的造成的伤害都是100%的。很久以前，我曾认为这个概念并不高明， 除了速战速决，不见得有什么好处，但事实上，“出圈即败”的危险给游戏加分不少。因为“出圈即败”的危险度太高了，无形中给游戏增加了一个“定位”的玩法；也就是，玩 家必须在打击对手的同时稳住自己的位置，以免被推出圆圈。
再举一个更直接的例子，任何时候你采取阻挡动作，你就得到一定的复原量。此时，你的恢复速度会领先于正在进攻的对手，所以在下一次进攻时，你在时间上有可能先出手。这 是你的优势，因为如果你们双方都打算发动相同速度的进攻，你的角色会赢（因为它会先行动）。你的阻挡动作的成效就在这里表现出来了，但这个效益是转瞬即逝的，可能仅仅 过了一秒，优势就不复存在了。
这里我有一个想法，就是把完全的滑坡效应（通常是恶性的）变成有限的滑坡效应（通常是良性的）。双方玩家一开始均持有相当的资本去购买单位。当你的单位被摧毁后你的资 本就会得到偿还。一方面，偿还需要一定的时间，另一方面，重新生产新单位需要一定的时间，这两方面意味着损失单位确实产生了消极影响，但这种劣势会渐渐消失，这与格斗游戏中的被击倒是一样的。即时策略游戏《World in Conflict》正是这么做的，不过我本人没有玩过。
我说这些的目的不是评判《World in Conflict》这款游戏好不好，或者讨论上述的“恢复系统”可取不可取。我只是想表明，如果你能努力研究一下，消除RTS中的滑坡效应还是 可能的。那些非常乐衷于此的人可能会想出更高明的解决方案吧，然后一款更高深的游戏就此诞生。
无限恢复实际上是默默地帮助了失利的玩家。我想对两类效应加以区别。其一，当你落后时，无限恢复就是一股扭转不利形势的力量。《虚幻竞技场》中的大男孩增变基因就是一 个例子。在FPS模式下，当你杀死一个敌人后，你会变得更肥大但更易被击中。当你挂了，你会变得更瘦小但更难被击中。所以如果你一死再死，你就会越变越瘦小。注意，虽然你 挂了N次，仍然在损失（你的得分也没用），但你确实获得了优势（更难被击中）。
相似的例子也出现在《Mario Kart》所有版本中。你越是落后，你得到的道具就越强大。最后，你可以得到强大的蓝海龟壳，这个道具能够自动对准跑在最先的赛车开火。同时， 跑在最前的赛车只能得到最差的道具。
任天堂DS的《Advance Wars: Dual Strike》也有相似的特点。双方的仪表上各系有一个强大的“标记攻击”。当你被攻击时，你的仪表填满速度将是平时的二倍，所以落后的玩家 会有更快的速度来发动进攻，这样，他自然就有机会恢复。
在以上三个例子中，游戏中存在一个“扶弱惩强”的力量。这个力量存在的积极意义在于，拉近了玩家之间的差距，削弱了前面犯下的错误造成的影响。也就是说， 在《Mario Kart》中，这股力量可能太过极端，或者说创造了一种奇怪的人为作用，如避免某位玩家长期占据比赛的第一名。而在《Advance Wars: Dual Strike》中，标记进攻的效应可能过 大，使其始终支配着游戏。撇开争议不说，这个概念仍然是合理的，运用得好的话，可以让玩家之间的差距更接近、比赛更刺激。
另一种无限恢复走了极端，这是比较少见的。所谓过头的无限恢复就是，当你落后时，这个劣势不仅是扶了你一把，而且等于是直接把你拉到领先地位。我认为最典型的例子就是 《Puzzle Fighter》。
个人认为，在我担任《Puzzle Fighter HD Remix》首席设计师以前，我就认为《Puzzle Fighter》是迄今为止最好的益智游戏。这款游戏看起来够水准——玩家各有一个面板接着 落下的棋子。玩家要用游戏中的四个同色碎片构成更大的单色矩形（能量宝石）。你之后可以用碰撞宝石将那些矩形破坏掉。你打碎的越多，你丢到对手一边的垃圾就越多。当你 的一方“封顶”，你就输了。
促成《Puzzle Fighter》中的无限恢复（极端版）有若干因素。首先，各个“角色”（共计11人，包括神秘角色在内）都有不同的“空投特征”，即当该角色粉碎己方的矩形时投 向对手的色块特征。例如，Ken的空投特征依次是水平红排、水平绿排、水平黄排和水平蓝排。每次Ken向对手投出的色块不多于6个时，就是一个水平红排；而当Ken投出12个色块 时，就是一个红排再加一个黄排。因为敌人知道这点，所以可以早做打算，将Ken的进攻转化为自己的优势。比如，当你向对方投色块时，这些色块会变成“反击宝石”，不能马上 被破坏，也不能组合为致命的能量宝石。过了五次行动，反击宝石就会转变为常规宝石。
另一个非常重要的特点是，在屏幕上位置越高的能量宝石破碎后，造成的破坏（投出反击宝石）会比下层的宝石更大。所以想想这款游戏的实际伤害是怎么样的吧。进攻其实只是 暂时性伤害，直到反击宝石转变为常规宝石。此时，对手可能会将这些宝石组合进自己的宝石中，因为对手知道你的空投特征。即使对手不能以这种方式从你的进攻中受益，他仍 然可以通过破坏你投给他的所有东西而“逃出升天”。对手的屏幕填得越满，反过来轰炸你的炮弹就越多。而且，因为对方快撑不住了，他的攻击会因为高度带来的额外效应而呈 现最大的伤害。越是高端的宝石，破坏后释放的杀伤力更大。
《Puzzle Fighter》具有极其罕见的特点，即“几乎失败”正是“几乎胜利”。比如说你破坏了大量能量宝石，给对手以重大打击。你自己的屏幕几乎被清空了，那么你就赢了对 吗？而对方的屏幕几乎封顶了，他输了，对吗？好吧，他只是挣扎在失败的边缘，但他拥有所有的弹药和额外优势，而你这一边却无所防御，你的对手同时处于“失败”和“胜利 ”的边缘。确实非常奇怪吧！
玩《Puzzle Fighter》的最好策略就是非常小心地规划自己的宝石，不要一次打到底。不然你就是反过来帮对手一把了。你得存着一些用来打击对手。你的对手总是有足够的进攻 来杀掉你，所以你得有足够的防卫。无论一开始局势如何有利于对手，运势也会一定程度上向你倾斜。只要不到最后一刻，输赢就没有定论。这款游戏被戏称为“卷土重来”，因 为刺激总是持续到最后一秒。
“滑坡效应”是对落后者的惩罚，让他们落得更后面。如果不加抑制，会使游戏预先区分出真正的胜利者，结果必然是损害游戏玩法，让玩家倍感无趣。虽然格斗游戏缺少这种彻 底的滑坡效应，但确实存在若干临时性、有限的滑坡效应，从而增强了玩法。这种受限的滑坡效应可能也存在于其他类型的游戏中，但在未来的游戏设计中，设计师们可以有意识 地采用这种形式。最后，无限恢复，即滑坡效应的对立面，是一股帮助落后玩家、阻碍领先玩家的力量，从而缩小竞争的差距。如果使用不当，这个属性非常容易走极端；但如果 使用得当，游戏将会更加好玩刺激。《Puzzle Fighter》将这一概念运用得淋漓尽致，从而给玩家带来一种“若输若赢”的感觉。
Game Design Profile: Slippery Slope (Part I)
by Brice Morrison
[Editor: In this guest post from David Sirlin, he discusses a common design that shows up often in games called the slippery slope, and how it works.]If a game has slippery slope, it means that falling behind causes you to fall even further behind.
For example, imagine that every time your team scored in basketball that the opponent’s team lost a player. In that game, falling behind is doubly bad because each basket counts for score AND it makes the opposing team less able to score points of its own. The actual game of basketball does not have this screwy feature though, so real basketball does not have slippery slope. Scoring in real basketball puts you closer to winning but does not at all hamper your opponents’ ability to score.
Slippery slope is another name for positive feedback, a loop that amplifies itself as in a nuclear reaction. Because people confuse the terms positive and negative feedback so easily, I prefer the more descriptive term slippery slope.
Slippery slope is usually a bad property in a game. If a game has a powerful slippery slope effect, that means that when one player gets a small early lead, he is more likely to get an even bigger lead, which in turn makes him more likely still to get yet an even bigger lead, and so on. In a game like this, the real victor of the game is decided early on, and the rest of the game is futile to play out (or to watch).
StarCraft and Chess do have slippery slope. They manage to be good games anyway, despite this anti-climactic property. In Chess, when a player loses a piece, his ability to attack, defend, and control space on the board is slightly reduced. Sure, there are many other factors in Chess–positioning, momentum, pawn structure–that determine if a player is actually “losing,” but losing a piece does have an effect. Clearly, losing a lot of pieces, say 8, puts a player
at a significant disadvantage. It’s pretty hard to make a comeback in Chess, and a game is usually “won” many, many moves before the actual checkmate move.
This is why there are a lot of forfeits in Chess. Good players don’t actually play out the pointless part of the endgame when they recognize the opponent will definitely win. Chess players would say that forfeits being a regular part of the game is fine and not awkward, but it’s a disappointing quality compared to games without slippery slope. Still, Chess is a pretty good game anyway.
This guy just lost a Chess piece.
StarCraft also has slippery slope. When you lose a unit, you are penalized doubly. First, you are closer to losing (having no units at all is so crippling as to be virtually the same as the actual loss condition of losing all your buildings). Second, you are less able to attack and defend because the unit you lost was not just part of a score, but also part of the actual gameplay of attacking and defending.
In basketball, the score is completely separate from the gameplay. Your ability to score points doesn’t depend at all on what the current score is. You could be ahead by 20 points or behind by 20 points and have the same chances of scoring more points. But in StarCraft (and Chess), the score is bound up with the gameplay. Losing units pushes you closer to loss AND makes it harder to fight back.
StarCraft has even more severe slippery slope when it comes to the game’s economy. Imagine that your opponent rushes you (sends an early attack to your base) and you fend it off. Let’s say you each lost about the same value of units in the exchange, except that you also lost one worker unit. In a different type of game, this might equate to being one “point” behind. But in StarCraft, that can be a crippling loss because gathering minerals is nearly exponential. Your opponent is ahead of you in the resource curve, increasing his earnings faster than you are. You’ve fallen down a very slippery slope
here, where an early disadvantage becomes more magnified as the game goes on.
Fighting games don’t usually have slippery slope. In Street Fighter, for example, your character still has all of his moves even when he’s about to lose. Getting hit puts you behind in life totals (in “score”) but doesn’t limit your gameplay options in the way that losing a piece in Chess does or losing a unit in StarCraft does. An unusual example of a fighting game that does have slippery slope is Bushido Blade. In that game, getting hit can cause you limp around or lose the use of an arm. This is extremely rare in the fighting game genre though, and for good reason.
While it might be “realistic” for a nearly dead character to limp, move slowly, and have generally less effective moves, it’s not fun. (At least in Bushido Blade’s case, this part of the game lasts only a couple seconds, then you lose.) Meanwhile in Street Fighter, comebacks are frequent and games are often “anybody’s game” until the last moment. Street Fighter does have some very minimal slippery slope aspects (if you’re very near death you have to worry about taking damage from blocked moves which aren’t a threat if you have full life), but overall it’s pretty “slippery slope neutral.”
There is one fighting game that stands out as an exception: Marvel vs. Capcom 2. In this game, each player chooses 3 characters. At any given time, one character is active and on-screen, and the other two are off-screen, healing back some lost energy. The off-screen characters can be called in to do an assist move, then the jump off screen again. The main character can attack in parallel with the assist character, allowing for a wide variety of tricks and traps. The player can switch the active character at any time, and he loses the game when he loses all three characters. But here, slippery slope rears its bitter head. When one player is down to his last character and the other player has two or even all three of his characters, the first player is at a huge disadvantage. The first player has can no longer attack in parallel with his assists, which often means he has no hope of winning. Comebacks in MvC2 are quite rare and games often “end” before they are technically over.
Fighting games with “ring out” such as Virtua Fighter and Soul Calibur as especially devoid of slippery slope properties. In these games, a player instantly loses if his character is ever pushed out of the ring, no matter how much energy he has. Basically, no matter how far behind you are, no matter how close you are to losing, you always have a 100% damage move: ring out. Long ago, I thought this concept was “cheap” and served only to shorten games while adding little benefit, but actually the threat of ring out adds quite a bit to both these games. Since the threat of ring out is so great, another whole element of positioning is added to the game. A player must fight both to do damage to his opponent, and fight for position to avoid ring out.
Limited Slippery Slope
Fighting games do have very localized, limited kind of slippery slope that’s actually a good quality. If a game truly has no slippery slope whatsoever at any point, then it can feel like a series of disconnected decisions. It’s interesting though, if a decision you make at one point in a game echoes forward through time, and can influence later moves in the game. The problem is if this influence is allowed to snowball into a greater and greater advantage.
In limited slippery slope, there is a cap on how far you can slip and the effect is temporary. In Street Fighter, getting knocked down (hit by a sweep) does have a bit of slippery slope. You lose health (“score”) but you also have temporary limitations on what your character can do. Your character falls down, then gets up into what is usually a isadvantageous situation. The two things that are important about this are: 1) after the knockdown is over, you regain all your moves and 2) you cannot get doubly knocked down.
Ken is at a temporary disadvantage here from being knocked down, but the disadvantage can’t snowball into deeper levels of knockdown (there aren’t any) and it fades with time.
Hitting the opponent with a sweep does echo forward through time, but this advantage is reset soon after and can’t snowball into “getting REALLY knocked down” because there is no such thing as degrees of knockdown. If you are already knocked down, you can’t be knocked down “even more.”
Another example is backing the opponent into the corner (the edge of the stage). If you do this, you have a natural advantage because the opponent has fewer movement options. But again, there’s a limit here. Once the opponent is in the corner, he can’t be “more in the corner.” There’s a limit to how disadvantaged he can get.An even more basic example is anytime you block a move that has a fair amount of recovery. In these case, you recover from your block stun before the opponent recovers from his move, so you have a few frames to act first. This gives you an advantage because if you both try to do a move of the same speed, yours will win (it will start first). Your good decision to block echoed forward into the future, but the effect is very fleeting. Even one second later, this advantage fades.
So fighting games are full of small, temporary slippery slope effects that actually help the game. And yet, on the macro level, they do not have the real kind of slippery slope, the permanent kind that snowballs until the game ends. Compare this to Chess where you don’t just get your captured pieces back a few turns later.
And RTS Without Slippery Slope
Here’s an idea for turning the full-on slippery slope (usually bad) into the limited kind (usually good). Both players start with the same amount of resources to buy units. When your units are destroyed, your resources are refunded. A delay in the timing of this refund combined with the build-time for making new units means that losing units really is a disadvantage, but that the disadvantage fades over time, similar in nature to getting knocked down in a fighting game. The real-time strategy game World in Conflict does exactly this, but I’ve never actually played it.
My point here isn’t about whether World in Conflict is a good game, or even whether the exact refund system stated above is good. It just shows that it is possible to remove slippery slope from an RTS if you try hard enough. Someone very dedicated to that problem could probably come up with an even better way to remove it that results in a deeper game, rather than a shallower one.
Readers, have you used a slippery slope in a game you’ve developed? How might you use (or avoid using) a slippery slope?
Game Design Profile: Perpetual Comeback (Part II)
by Brice Morrison
[Editor: In this guest post from David Sirlin, he discusses the sister design to a slippery slope, the perpetual comeback, and how it works.]The opposite of slippery slope, I call perpetual comeback. That’s just a more descriptive term for negative feedback. (Also, negative feedback sounds like a bad thing, but it’s usually a good quality in games, so it’s helpful to have a term that doesn’t sound negative.) A thermostat uses negative feedback to keep the temperature of a room from spiraling out of control.Perpetual comeback, then, is a quality in which being behind actually gives you an advantage. I’d like to draw a distinction between two types of this effect, though. In one, when you are behind, a force pushes on you to help improve your position. An example of this is the Fatboy mutator in Unreal Tournament. In that first-person shooter mod, when you kill an enemy, you become fatter and easier to hit. When you die, you become skinnier and harder to hit. Multiple hits magnify the effect, so if you die over and over you get skinner and skinner. Note that even if you die a lot, you are still losing (your score is not helped), but you do have an advantage (harder to hit).
Beautiful, but dangerous.
A similar example is any version of Mario Kart. The further behind you are, the more powerful the items you get. In last place, you can get the powerful blue turtle shell which has homing powers to zero in on the first place racer. Meanwhile, the first place racer gets only weak items.
Advance Wars: Dual Strike on the Nintendo DS has a similar feature. Each side has a powerful “tag attack” that’s tied to a meter. When you get attacked, your meter fills up at twice the rate as usual, so the losing player will have faster access to this powerful attack, giving him a chance to make a comeback.
In all three of these examples, the games have a force that help out players who are behind and hinder players who are ahead. This is generally a good type of force to have, because it makes games closer, and small early mistakes are not crippling. That said, maybe the effect is too extreme in Mario Kart, or maybe it creates strange artifacts such as avoiding 1st place on purpose for most of the race. And the power of the tag attacks in Advance Wars might be too extreme, making them dominate the game. Tuning issues aside, the concept is still sound and when it’s done right, it can make matches closer and more exciting.
Perpetual Comeback Extreme
There is a different type of perpetual comeback that is far more extreme and far more rare. That’s when getting closer to losing doesn’t JUST give you helping hand, but instead actually puts you ahead. I think the best example of this strange property is Puzzle Fighter.
Puzzle Fighter is, in my opinion, the best puzzle game ever made and I felt that way long before I was lead designer of Puzzle Fighter HD Remix. The game seems standard enough–it’s one of those games where each player has a basin that pieces fall into. There are four different colors of pieces, and you try to build big, single colored rectangles (power gems). You can then shatter those rectangles with special pieces called crash gems. The more you break, the more junk you drop on the opponent’s side. When your side fills to the top, you lose.
Several factors come together to create perpetual comeback (the extreme version!) in Puzzle Fighter. Firstly, each “character” (there 11 to choose from, including secret characters) has a different “drop pattern.” A drop pattern is the pattern of colored blocks that a character will send to his enemy when that character shatters blocks on his own side. For example, Ken’s drop pattern is horizontal row of red, followed by a horizontal row of green, then yellow, then blue. Every time Ken sends 6 or fewer blocks to his opponent, he’ll send a horizontal row of red. Every time Ken sends 12 blocks, he’ll send a row of red, then a row of yellow. Since the enemy knows this, he can plan for it. He can build his blocks such that Ken’s attack will actually help rather than hurt. There’s one catch: when you send blocks to the opponent, they appear in the form of “counter gems,” which can’t be broken immediately by normal means, and can’t be incorporated into deadly power gems. After about 5 moves, the counter gems change into regular gems.
The other very critical property is that power gems broken higher up on the screen do more much more damage (send many more counter gems) than gems broken at the bottom of the screen. So consider what attacking is actually like in this game. Attacks are really only temporarily damaging, until the counter gems turn into regular gems. At that point, the opponent will probably be able to incorporate the gems into their own plans, since the opponent knows your drop
pattern. Even if the opponent isn’t able to benefit from your attack in that way, he can still “dig himself out” of trouble by breaking all the stuff you sent him. By filling up his screen most of the way you’ve basically given him more potential ammunition to fire at you. What’s more, as he is nearest to death, his attacks will be the most damaging due to the height bonus. Gems broken at the very top of the screen do significant damage.
Puzzle Fighter has the extremely unusual property that “almost losing” looks exactly like “almost winning.” Let’s say you break a whole slew of power gems and send a large attack at your opponent. You’re screen is now almost empty. You’re winning right? His screen is nearly to the top–almost full. He’s losing, right? Well, he is on the verge of losing, but he has all the ammunition and he has the height bonus, whereas you have almost nothing left to defend with. In effect, your opponent is both “losing” and “winning” at the same time. Very curious, indeed!
Ken (left) was close to losing, but he got the yellow crash gem he needed just in time. Donovan (right) will lose.
It turns out the best way to play Puzzle Fighter is to very carefully never attack until you can make it count. All those little jabs you make just help the opponent in the long run. You’ve got to save up for a huge, 1-2 punch. You need to send a big attack that almost kills them, then immediately send another attack that finishes them off. 1, 2! The point is that Puzzle Fighter is a high energy, edge-of-your seat game. Your opponent very often has enough attack to kill you, so you have to have enough defense to stop them. Whenever the scales start to tip in your opponent’s favor, they have also, weirdly, tipped in your favor as well, in some sense. A game of Puzzle Fighter is never over until the last moment. Comebacks are the name of the game, and the excitement goes to the very last second almost every time.
Slippery slope is a force that punishes players who fall behind, making them even more likely to fall further behind. Left unchecked, this makes for matches where the real victor is decided long before the game actually ends, leading to either boring endgame play, or lots of forfeits. While fighting games lack this overall slippery slope, they do have several forms of temporary, limited slippery slope that improves gameplay. This limited slippery slope probably exists in other genres as well, but could be a conscious design choice for future games. Finally, perpetual comeback, the opposite of slippery slope, is a force that helps losing players and puts the brakes on winning players, making for close matches. This property can easily go wrong if tuned improperly, but if done well, it leads to closer, more exciting matches. Puzzle Fighter takes this concept to an extreme, by making winning look almost the same as losing.