Here is the full list of all 13 Boomerang Fu trophies - there are 10 bronze, 2 silver and 1 gold.
Killed an opponent after dying
Mastered the disguise powerup
Telefragged an opponent
One of your "teammates" killed you
Killed many opponents with the telekinesis powerup
Dodged a lot of boomerangs
Regularly killed yourself with the explosive boomerang
Killed a lot of enemies with fire
Shattered a lot of frozen enemies
Squishing several opponents with moving blocks
Killed opponents while unarmed
Spent a lot of time hiding in the bushes
Neither the best nor the worst at anything in a match