In the worldwyrm mission, Omga (Thunderdrake) is on level 42 i think so if you use Time Magic: Stop or Babus` Stillness spell on Omga, you can have your weaker units attack him and will get massive expeirience!! If you only bring one weak unit and level him/her up a lot and u want another unit to get leveled up by omga. Flee and except the mission again. I hope this helps. :)