Cheat Mode

At the "Extras" menu, select the "Promotions" option. Then, enter one of the following codes by selecting the corresponding aliens to unlock the corresponding upgrade.

Gravattack upgrade
Enter Feedback, Fourarms, Diamondhead, Bloxx as a code to unlock the Gravattack upgrade.

Wildvine upgrade
Enter Gravattack, Eye Guy, Arctiguana, Wildmutt as a code to unlock the Wildvine upgrade.

XLR8 upgrade
Enter Shocksquatch, Gravattack, Arctiguana, Diamondhead as a code to unlock the XLR8 upgrade.