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