for deal whit the colossus,just put in your army all the following unit at max lvl. beast rider whit poison orb,paladin whit platinum sword then all these following whit platinum swords:whitch,elf archer,centaur and succubus. destroy the minions behind the colossus and keep him alone during the fight,make retreat your ranged unit and use spell agais the colossus and his minions,also block it whit 2 altars and 2 wall AND MOST OF ALL CHECK THAT YOUR HERO REMAIN IN THE OTHER SIDE OF THE MAP!
for me the game indeed is challenging , but the worm should recover his healt by eating man and animal, or a regenerative power up, good game for who want a challenge ^^
little tips, once reached da level 12 and above you may encounter HUGE unite black dragon(liv.14),angel(liv.12) for deafeat them shoot o their head whit at least the tower tat level 4 they could be even stunned for this
 "Epic War 5"){kind=icon}
 "Epic War 4"){kind=icon}
 "Epic War 2"){kind=icon}
 "Death Worm"){kind=icon}
 "Burrito Bison"){kind=icon}
 "Epic Quest"){kind=icon}
 "Dungeon Defender"){kind=icon}