From the Super Mario Wiki
Little Mousers, also known as Squeeks or Mowz, are a species of small, mice-like creatures who wear bandanas that obscure their faces. Their English name refers to another mouse-like enemy, Mouser, who was introduced in Super Mario Bros. 2.
Super Mario World 2: Yoshi's Island / Yoshi's Island: Super Mario Advance 3
The first appearance of Little Mousers was in Super Mario World 2: Yoshi's Island, were they appeared infrequently as enemy creatures who would try to steal a Yoshi's egg and scurry away with it, into their burrows. Little Skull Mousers also appear - they are just like normal Mousers, except they wear skulls on their heads and cannot steal eggs.
Yoshi's New Island
Little Mousers, along with Little Skull Mousers, both under their original name, also appear in Yoshi's New Island. They act the same as their first appearance.
Mario Kart: Super Circuit
Little Mousers later appeared in Mario Kart: Super Circuit as obstacles in the Cheese Land course. However, they are left absent in the course's reappearance in the Animal Crossing x Mario Kart 8 DLC pack.
Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Little Mousers were renamed Squeeks and were shown to be one of the primary inhabitants of Rogueport and Rogueport Sewers; a white Squeek, known as Ms. Mowz also appears in Paper Mario: The Thousand-Year Door as an optional partner of Mario.
Mario Party series
Mario Party Advance
In Mario Party Advance, a Little Mouser named Mouser appears as the boss and owner of the Duel Tower. He challenges the player to the game Chicken!. If the player wins, he receives the minigame. The ending said that he was bummed that Whomp left the Duel Tower.
Mario Party 8
In Mario Party 8, Little Mouser (called Mowz) is a recurring character. It first appears in King Boo's Haunted Hideaway. If a ? Space is landed on inside the mansion, Mowz will let the player spin a wheel with a pinball inside. Depending on which one of three holes on the wheel the ball lands in (Coins, Star, or Candy), it will steal an item from a random opponent for the player.
Another appearance of Mowz is in Shy Guy's Perplex Express. It stole Holly Koopa's candy, and when landing on a ? Space (it's one of the ones above the train) a Shy Guy will come and tell the character about the incident. Then he'll tell the character who the suspect is (Bandit can also be the one who stole the candy). If the player correctly remembers which car Mowz was on, they will be rewarded with 20 coins (10 in Duel Mode).
Names in other languages