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.
Being on time to things
Killed many opponents with the telekinesis powerup
Telefragged an opponent
One of your "teammates" killed you
Squishing several opponents with moving blocks
Shattered a lot of frozen enemies
Dodged a lot of boomerangs
Mastered the disguise powerup
Spent a lot of time hiding in the bushes
Killed a lot of enemies with fire
Killed an opponent after dying
Regularly killed yourself with the explosive boomerang
Killed opponents while unarmed