Here is the full list of all 23 Lethal League achievements.
Reach level 10
Hit three players in a row
Reach a ball speed of a hundred thousand
Reach a ball speed of one thousand
Get hit by your own ball
Reach a ball speed of two hundred fifty
Reach a ball speed of one hundred
Rally the ball back and forth for at least ten times
Hit two players in a row
Reach a ball speed of one million
Play a hundred matches
Play five hundred matches
Play one thousand matches
Beat the challenge mode with Raptor
Beat the challenge mode with Switch
Beat challenge mode with Candyman
Beat the challenge mode with Sonata
Beat the challenge mode with Latch
Beat the challenge mode without using any continues
Beat the challenge mode with every character
Bunt the ball at 1000 speed or above
Reach level 20
Beat the challenge mode with Dice