The left and right keys are used to move the character in that direction. The up key is used to jump and spacebar is used to attack/perform a particular action. Pressing Z key opens the alien selection screen.
Use your alien powers to defeat Dr. Animo. Hold down Z to enter the transformation panel. The spacebar activates special abilities. Ben punches, Wildmutt can detect hidden mines, Wildvine throws explosive seeds, Heatblast throws fireballs and Cannonbolt changes to ball form. You can use Wildvine to swing on branches by using the up arrow key and use Wildmutt to jump down on enemies.