From the Super Mario Wiki
Smeeches are pig-like enemies that appear in the game Super Mario Galaxy 2. They appear as pink winged creatures with two beady eyes and plump lips.
Smeeches' only method of attack is kissing and sucking Yoshi's lips, making him unable to use his tongue or eat fruits. If Yoshi tries to eat one, the creature will suck on his lips. They can only be defeated with a Spin or get jumped on. Also, they will flee from Mario or Luigi if they are not riding Yoshi. To get a Smeech off of Yoshi's mouth, Yoshi himself has to spin his head to make the Smeech vanish, dropping Star Bits. If Mario or Luigi dismount or get knocked off Yoshi, the Smeech will detach from Yoshi's mouth and hover away.
Smeeches are first encountered in the Yoshi Star Galaxy, ever since the first mission, Saddle Up with Yoshi. They are encountered later on in the Hightail Falls Galaxy, the Haunty Halls Galaxy, the Sweet Mystery Galaxy, and the Starshine Beach Galaxy.
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