No ents so far.
I guess, that finding royals in main arena should to the trick. 4th battle is the only hard one, so i'm gonna focus in finding the best possible start for a imp/mage game. Boots or armor to raise psyh ress or just royal thorns.
Well, just checked the stats. Thorns have a Def of 3 as for ancient ents 60
And 1400 HP!! Heh, i guess there's a reason that they don't spawn in main arena, because with Hagrid, this would be too overpowered.