Bonus characters

Successfully complete the indicated task to unlock the corresponding Boss:

Biker Ben: Defeat Biker Ben on Training Level 6.
Cavegirl Carmen: Defeat Cavegirl Carmen on Nature Park Mission 8.
Rabid Rabbit: Defeat Rabid Rabbit on Playground Mission 8.
Snorkel Jane: Defeat Snorkel Jane on Beach Mission 8.
Trooper Tim: Defeat Trooper Tim on Plaza Mission 8.