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