DoubleGJ, MoonBlaze, and wiivn all have good ideas imo.

Maybe wiivn's entry can be done for the most part using AngelScript and existing sprites? Though the modified sprites and screenshot gives the best practical example of all entries, the concept art for the Hermit Crab and Grim Reaper feel slightly more original using my imagination how they could work in-game. But that's what concept art's for I guess.

Good luck to the entrants!