If it is the one where he ate the trolls tin cans, then beat the troll by throwing or
kicking the bombs he throws at you.

Wii Gamer is right but u can also use shrek to pick up and throw bombs. Trolls show up a
lot in the game and on the last level you can use tnt. Also on the last level u should use
a buddy to help because 2 trolls are togther and help each other( unless if you hide and
make them throw bombs at each other. happens rarely.) After that there will be 3 together
so watch out but since i can do it so can you.

Oh sorry i forgot to use peace out. Peace Out:)