Super Paper Mario/Pit of 100 Trials Flipside

Check the floor you want to reach and see if you have met the requirements.

If you have all that, if you have Luigi go to Flipside B2, use super jump and hit the blue switch.

If you don't have Luigi, go to Flipside Outskirts, go down the pipe to your left, Go down another pipe to your left, find the hidden blocks with Tippi, jump across the blocks and hit the switch.

In every room there are a few enemies. One random enemy has the key. Kill the enemies until one drops a key. When you get the key, unlock and go through the door. Every tenth room you get a card.