BHB unofficially asked someone to make a cave troll FAQ, so here it is
Q: Where are cave trolls found?
A: They are found in caves in the bottom quarter of the world
Q: What do they look like?
(picture found at the blockheads wiki)
Q: Do they spawn with anything?
A: They spawn with two ice torches and one golden chest. As of 1.5 they also spawn with a trade portal.
They may occasionally spawn with only one ice torch, depending on where they spawn.
Q: Do they drop anything when killed?
A: When they are killed, you may receive a piece of ice armor, which you can wear. you will also get an achievement in game center when you first kill a cave troll:
Achievement: blue fury
Definition: defeat a cave troll
Points earned: 5
Way to earn: mine to center of the earth, mine sideways, find caves near center of earth, explore, find cave troll, defeat cave troll
Q: Do they harm you?
A: If you harm or get too close to them, they will harm you. If you run away when it walks towards you, it will continue to follow you until it hits you.
Q: How do i trap a cave troll?
A: You need to make a cave troll follow you to the designated location (make sure there are no narrow horizontal passageways) and then simply surround it in a block.
Q: A cave troll wont stop following me! How do I escape?
A: Go into a tunnel in which you need to crawl through, or get far enough ahead and block it off from you.
ADDED BY COMMUNITY:
If i missed any important points please tell me and ill add it