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