After some testing, it seems the best meta is to: (1) Use ice, (2.A) If wet, use wind (2.B) If burning, use ice again (2.C) If cold, use fire, (3) Repeat.

To my knowledge, Difficulty 4 seems impossible, because:
1) 2.B leads to opponent doing a fire loop (you're locked to doing wind or ice to remove burning, and neither does extra dmg because their ice was removed)
2) 2.C leads to opponent doing an ice loop (you're locked to doing fire to remove cold, but ice->fire doesn't deal double damage, and even if it did, after 1st atk, you can't do any more reactions, because none remove cold)

Overall, a very cool game! If you can optimize the world in the background to not eat all the PC's resources, tinker with the reactions a bit, and maybe add a few more different opponents with different strategies, you've got yourself a full package of a game! I thoroughly enjoyed, thanks for make!