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