Quests and puzzles!

How? According to my calculations, it takes at least HP*1000 rounds, because the butterfly deals 1 damage.

The Fairy can be enhanced with skills and spells – the damage will increase to approximately 16, with an attack every other turn. Unless, of course, this is prohibited by the conditions – but then it becomes a task of “how to break through a wall with your forehead” – and after a thousand attempts, the wall might still not break.
Regarding the hero's level – starting from level 75, glitches begin, immediately jumping to level 88, negative experience, etc. That is, level 108 is more of a theoretical limit, and stable development occurs up to level 75. The same applies to skills – the theoretical limit is 127 (it is added, but not displayed), but you cannot set more than 99, and increasing it (artifacts, libraries) does nothing – the damage does not increase. For example, after destroying 4000 dragons and gaining experience, the attack suddenly dropped from 99 to 1.