Small guide on how to beat the colossus + if you think its helpful use up to two Epic units, then use the two strongest range units you have and equip the last three slots with quick moving melee units. Your epic units are only used for clearing the way for your weaker units, then the fast moving melee units are to stop the colossus from moving as much as possible while your range units just whittle down his life until you win, do not use any regen spells use rage at all times.
Thank you, I still need to figure out how to add the other levels in there.