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
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
Mastered the disguise powerup
Killed a lot of enemies with fire
Killed opponents while unarmed
Spent a lot of time hiding in the bushes
Killed an opponent after dying
Shattered a lot of frozen enemies
Squishing several opponents with moving blocks