From the Extras menu, select Promotions and then select the alien images outlined below to fully upgrade XLR8, Gavattack and Wildvine.

Effect	Password
Gravattack	Feedback-Fourarms-Diamondhead-Bloxx
Wildvine	Gravattack-Eye Guy-Arctiguana-Wildmutt
XLR8	Shocksquatch-Gravattack-Arctiguana-Diamondhead