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