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.
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
Being on time to things