Easy "Old School" Achievement...
	Play as Doombox...
	Various Steam Achievements...

Start a Versus mode game. In the match options, uncheck "Ball Tagging" so that the ball is not tagged upon being hit. Then, just get hit by your own ball.

If you select certain characters in the correct order you gain the ability to play as the challenge mode final boss (Versus and challenge mode only)

Code	Effect
Sonata>Raptor>Switch>Candyman>Raptor>Dice>Latch	Select Doombox

Complete the indicated task to unlock the achievement.

Achievement	How to unlock
1st Division	Play one thousand matches.
2nd Division	Play five hundred matches.
3rd Division	Play a hundred matches.
Ace Player	Reach level 20.
Bats In The Dark	Reach a ball speed of two hundred fifty.
Boomhammer Beatdown	Beat the challenge mode with Sonata.
Chrono Warp	Reach a ball speed of one thousand.
Chrono Warp Cluster	Reach a ball speed of a hundred thousand.
Clutch	Bunt the ball at 1000 speed or above.
Doombox Slam Dunk	Beat the challenge mode without using any continues.
Double Play	Hit two players in a row.
Firmware Remix	Beat the challenge mode with Switch.
Full House	Beat the challenge mode with every character.
Grand Slam	Reach a ball speed of one million.
Lethal Rivals	Rally the ball back and forth for at least ten times.
Mass KO Production	Hit three players in a row.
Old School	Get hit by your own ball.
Rifle Strike	Reach a ball speed of one hundred.
Rookie Player	Reach level 10.
Sweet Victory	Beat challenge mode with Candyman.
Underground Revolution	Beat the challenge mode with Latch.
With A Twist	Beat the challenge mode with raptor.