From the Super Mario Wiki
Mini-Ravens are small Ravens that only appear in a few levels in the game Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3. When Yoshi eats them, they are automatically digested without being turned into a Yoshi Egg. Like their larger cousins, Mini-Ravens can climb walls and ceilings. Mini-Ravens don't appear in any other Yoshi game.
Super Princess Peach's standard Ravens are extremely similar to Mini-Ravens, being small and giving no Vibe energy if attempted to be absorbed (in a similar manner to how Yoshi could not produce eggs upon eating Mini-Ravens). If these Vibe Island Ravens are to be thought of as Mini-Ravens, then Sad Ravens can be considered a Mini-Raven sub-species.
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