Beat the 1st level
Beat the 2nd level
Beat the 3rd level
Beat the 4th level
Unlock the new character
Unlock a new item
Fully upgrade one of the characters
Unlock a third character
Kill 750 enemies
Kill 1500 enemies
Fully upgrade two of the characters
Unlock all items
Unlock the third character
Kill 2500 enemies
Kill 3000 enemies
Unlock a new character