Yeah that was planned, that's why the final stage looks different :D
If you're curious about the boss I'd planned, it was this:
Dryad Queen.
Innate: Poison heals Dryad Queen instead.
>19: Drain the opponent by the amount of poison on self.
>15: Double own poison.
>10: Poison self by the counter value.
>2: Poison self and increase the counter.