this is a very cheapo tactic i read in a low lvl guide.
According to that the yellow dragons take off 1/4 of the enemies FULL hp(not current).Meaning if you make your group monster trainers,Catch 4 yellow dragons and release them he will go down.

If u dont wanna go cheap then do like i did.Cast golem
Cast quicky kill spells(those lvl 3 ones) and whack.Cast golem all the time.