Avoid Traps:
Whenever you need to get through a room filled with traps, press Z to go into the Menu Screen to walk by them without getting hurt.

Dressing Room Access:
When starting the game, have at least 10,000 Meseta in a character's coffers (not in the bank). Note that any changes you make in the dressing room will cost 10,000 Meseta when you're done.

Spawn a Chair in Online Lobby:
While you're in the lobby, hold X and press A. To move forward press A; to make the chair disappear, press B.

Thanks to Revolution readers Amon, Erebus, and HammerHand!