Hydra Slayer
You are facing a nine-headed hydra. Your flaming longsword cuts five heads in each swipe (no more, no less), which will kill a five-headed hydra, but a larger one will regrow two heads after each swipe. Your storm scythe cuts exactly seven heads, but it makes ten heads grow back if the hydra is not dead. Is it possible to kill the hydra? What if you also had a silver dagger, which cuts just one head, but makes five heads grow back?
Solution: It is impossible without the silver dagger (the number of heads always stays divisible by 3), but possible with the silver dagger, for example: 9 -> longsword -> 6 -> longsword -> 3 -> dagger -> 7 -> scythe -> 0.
If you liked this puzzle, and you also like dungeon crawling, Hydra Slayer is for you!
Hydra Slayer is a roguelike (randomly generated dungeon crawler), with unique combat mechanics based on the puzzle above. It is challenging both at a short term tactical level (each hydra is a unique challenge, bumping into it with your weapon almost never works), and at a long term strategy level (you have to build a set of weapons which slays hydras effectively). While the early levels could be used to teach arithmetics and tactical planning in a fun way, building an effective set of weapons for late levels is a challenge even for expert number theorists!
Hydra Slayer currently features a tutorial, 5 player character races with distinct characteristics, 28 enemy types (10 common hydras, each in two varieties, and 8 special enemies), 28 types of equipment including rare artifact weapons with special properties (not counting material and size variations), 15 weapon materials, 18 types of magical items which help you in your quests, three game geometries to choose from, 8 level topologies on very deep levels (including the Möbius strip and Klein bottle), 11 level generators, and two endings (a small victory for quick challenges and more casual players, and a big victory for those who want more challenge).
The Steam version of Hydra Slayer includes online achievements and leaderboards, a “challenge” mode for short but very interesting games (much more unpredictable than the normal play), traps to lead hydras on, and Orbs which provide a powder/potion effect many times at the cost of a weapon slot!
游戏讨论
Steam User 12
这个游戏的难度很大部分建立在信息不够直观上，难以把实战转化成经验策略。冷门游戏指南又少，我是啃不动了。但作为对开发者zeno和他上一个游戏 HyperRogue 的支持，买了还是爽到。这里简单介绍一下我已掌握的情况，有猛男感兴趣的话可以试试。
游戏设计灵感来自希腊神话海格力斯击杀海德拉“砍掉的蛇头会重生”这一概念，然后就有了基本玩法：安排好随身携带的不同伤害武器的攻击次序，以最少的攻击次数斩落全部蛇头，而这需要武器伤害或者策略足够正好抵消海德拉因受伤不断规律性再生的蛇头数量（就像小学数学中泳池一边放水一边注水何时放干）。除了不同武器每刀斩落的蛇头数不同，还有属性相生相克提升运算决策的复杂度，以及多样的道具来应对游戏随机性可能会产生的仅靠武器无法解决的状况。
不过，HS首先是一个老派RL然后才是数学PUZ，这使得入门进阶需要掌握的信息更多更杂，其中很多还要以猝死为代价换取，比如应对后续关卡需要提前做的准备，包括武器伤害合理升级、武器属性微调、针对性道具积累等等。再加上开头提到的信息不够直观，“未知”对游戏过程有着绝对影响，成了高于解谜的存在。真实无从下手，有点急也有点生气。
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