From the Super Mario Wiki
The Hippo is a big, statue-like animal found in Super Mario Land 2: 6 Golden Coins and it appears in its own zone, the Hippo Zone. This creature releases Bubbles from one of its nostrils when Mario approaches it. Then Mario can go into the Bubble and be able to "swim" in air. The Hippo is not a true enemy; it only releases bubbles.
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