Here is the full list of all 13 Boomerang Fu achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
One of your "teammates" killed you
Telefragged an opponent
Killed many opponents with the telekinesis powerup
Being on time to things
Dodged a lot of boomerangs
Killed a lot of enemies with fire
Shattered a lot of frozen enemies
Killed an opponent after dying
Regularly killed yourself with the explosive boomerang
Killed opponents while unarmed
Squishing several opponents with moving blocks
Mastered the disguise powerup
Spent a lot of time hiding in the bushes