Merlin the Magic Mouse is a character from Looney Tunes and Merrie Melodies shorts - He is a magician mouse who has a sidekick (or better: magician's assistant), appropriately named Second Banana. It first appeared in Merlin the Magic Mouse a 1967 short.
Merlin is a stage magician (he usually preferred to be called a prestidigator, though he could never pronounce this correctly) who traveled around for work with Second Banana. Much of the humour of the character derived from the fact that, while he was often regarded as a cheap stage magician, he knew some very real and powerful magic tricks. His magic words were typically "Atascadero Escondido!"