As Wario, you have to talk to the toad in the secret second basement
of the castle, which is now accessible through the empty pillars pool, by doing Wario's ground pound. The toad will tell you to go buy him a taco. So go to the nearest take away tex-mex restaurant, and ask them to make an ULTRA SPICY FIERY TACO
(please make sure it is both ULTRA SPICY
, because if it's not, the toad will murder you and everyone you love, MWAHAHAHAHAHAAAAA
When you give it to the toad (by forcing the taco through the screen) he will become very
thirsty (because of the spice), so use Wario's special peeing ability
to calm the poor guy's thirst. Once you do that he'll open a secret door which leads to...
I quit hacking. Don't hack Nintendo ROMs, kids! ROM hacking is illegal an very very rude for the original creators!