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