Mouse

Mice are encountered during the Grim Tales quest while the player is shrunk. The mouse's drops (bones, coins, and cheese) look relatively large on the floor, but return to normal size when picked up along with the message The object shrinks to your size as you touch it. and stay normal-sized if dropped again.

Unusually, the large drops do not stack on the floor; if a new drop would appear on the same tile as a previous drop, the new drop will fully replace the previous drop (this does not affect normal-sized drops).

Presumably the mouse is only about as large as a rat in absolute terms, but has a high combat level because the player is smaller.

These mice cannot be chased as vermin by a cat. The bones dropped by these mice can also not be crushed using a bonecrusher, due to their unique mechanic of dropping as a large version that shrinks when picked up.

Drop rates are estimated based on 863 samples from the Drop Rate Project, unless otherwise cited.