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I'm sure a solution exists.
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I don't think this is the case. In order to eliminate bots for a game-based blockchain you need to design a game that meets two criteria:
1) Bots can't "win" the game, or if they can earn some coins, it has to be many orders of magnitude less than a human playing the same game, otherwise someone can just run thousands of bots, right? You basically need a game version of the Turing test.
2) You need to have a game that, although bots suck at it, the results must be able to be easily and quickly verified by a computer. This is another wrinkle that makes point #1 much harder to achieve.
Afaik, a solution does not exist, and if you came up with one you'd probably be some kind of laureate or at least have a cushy CS professorship at MIT or something.
I'm also sure a solution exists. (One that could be of actual use for Huntercoin)
(*) my assumptions, didn't play or do source diving.
Motocoin uses block hash (*) to seed the RNG for creating a level, and when the first player has solved it, they submit the result: the complete player input,
keystrokes (*) with timestamps (*) measured in terms of ticks of the game's physics engine (*). Verifying a block means replaying the level to see if the submitted player input solves the level.
The standard example of a un-bottable game would be Nethack, but it takes at least some hours + expert skills to solve.
(result is also a bunch of keystrokes, quickly verified by a computer)
If the game is simpler (but still a turn based "roguelike" game) and bots can win, they need less time than a human, but more game turns.
Example: Angband bot, if very lucky: 10.000.000 turns, Human expert: 50.000 turns
If the game is too short (same turn based "roguelike" game) then bots can simply try every possible action and brute force (if it's possible to win in ~100 turns)
Example: You start as high level char in the deepest Angband dungeon level, but stripped of every possession: try to escape as fast as possible.
Huntercoin doesn't need the result for the next block, it could create a random "instanced area" once per day, hunters that would enter this area would be alone, playing a (local) single player game against (deterministic) computer controlled monsters. Only after winning, results get posted to the blockchain, and only after the day is over, the fastest winner (in terms of game turns) get coins. (game turns != Huntercoin blocks)
The number of game turns would have a (not too low) target value, fast win today == extra nasty dragons tomorrow.