From the Super Mario Wiki
“Thanks to thee, The Overthere is safe again.”
Whibbi is a Nimbi who helped Mario and his friends save the Overthere. He was first found encased in a block of solid ice, which implies that he had probably been frozen by Bonechill's icy breath, like many other Nimbis. Using his own Fire Breath, Bowser thawed the ice and thus released Whibbi. Then, Whibbi told Mario to find the Red, Blue and Yellow Orbs so he could rebuild the bridge to Grambi's palace and they could continue their quest.
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