Oh yeah I remember you said you didn't have it in lil's team well you need to move the block in front of the hole then go away untill the mouse runs out it will see the hole is blocked and try to run back to the other hole but before it gets there you kill it.
if its later just draw a really mess path and throw the boomerang when the mouse comes by. the boomerang is in a chest in the first dungeon. (not the temple of the ocean king thats the last dungeon)
Makin' a comeback!