I just finished playing impossible Paladin with just thorn hunters and thorn warriors. Got the Crown (+100% damage), Hagrid, botany diploma and thats all what i needed. The battle is over about 4-5 turns, ressurection just takes time.
First boss is easy as it gets, spider boss was very time consuming
used the "magic axe" tactic and from there on, it got a somewhat boring, because thorns are REALLY overpowered with Hagrid and his ress ability - 72-111 thorns in every turn
Finished in day 1, score was 1110 something.