Full power
During game play, press A, B, then hold Left and press R, A, B, X, Select. Highlight the Swamp icon. It will not turn red if code entry was successful.

World select
Pause game play in conquest mode. Move the pointer over the map. Hold L and press A. Hold R and press Y, B, X, A, Select. Release R. Highlight the Armageddon icon and press A. Game play should remain paused. Highlight the Conquest icon and press A. Press X or B to choose a world.