Coco the Troll is first encountered in level 4-8, where he demands a payment for passing through the Valley of the Myst. "You must pay the troll toll to get through this hole," "Pay the troll toll to get past Coco the Troll!" The heroes have no intentions of paying, and that moonstone in his belly looks very enticing to Des. The player has to make it through the Valley of the Myst while protecting the wizard, who is enchanted by the troll. Trolls have a large amount of HP and powerful attacks, so its best to try to hit them from a distance with specials.
Coco the Zombie Troll comes back to haunt the player in level 5-3 when you are trying to escape back to the castle after you resurrect the Phoenix. Lord Magma brings him back to life and grants him a large army of death walkers.
The Troll will spawn and not move until he is attacked. He is followed by multiple Imp monsters. Trolls are more extreme versions of gargoyles, having more bulk and attack power, but more expensive and with longer reload time.
When you first encounter the Zombie Troll, you cannot harm it with any spells in your book, since Coco states that he cooked up a spell to protect him from your spells.
In Monster Wars his special is changed to slamming the ground with his arm, which is similar to the Tier 4 Golem's special.
In Monster Wars he is encountered in level 4-7. Before the level starts, Coco tries to take the monsters' souls, but is convinced by Funny Bones that monsters don't have souls and that he should instead take the souls from the approaching heroes.
In Monster wars, trolls' special attack is to smash the ground hard and create a shockwave. Their Tier 2 (zombie trolls) smack the ground twice. Trolls are alternative to gargoyles stat wise. Also, you could choose both of them to create a good tanking force. In order to unlock them you have to "pay the troll toll" by paying 4 soulstones to him in the armory.