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)

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).

You can download Hydra Slayer 18.1 for free (the paid version is the same at this moment). The Steam version adds online achievements, online leaderboards, trading cards, cloud-based save, automatic updates, and convenience.

Screenshots show the many possible graphical modes supported by the NotEye frontend, and by Hydra Slayer (can be played in hex or a normal square board). One of the screenshots shows the optimal strategy (sequence of weapon attacks) against a 105-headed golden hydra, at some point in the game (level 11). If this looks too difficult for you, note that the game starts much easier (new weapon types are introduced gradually), and you don't have to always use the optimal strategy to be successful :)