The Mutant Fuzz is Fredric Effects' version of the Os Mutantes (Regulus VIII) fuzz.
The Regulus VIII is similar in topology to a silicon Fuzz Face, but with a more gritty and trebley character. The Mutant Fuzz is pretty much a straight clone with some added power and RF interference filtering - so it won't pick-up the radio like the originals sometimes do! The level of gain is fixed at 'just right', although you can roll back your guitar volume pot to clean up a bit. The tone control is a switch for hi/low. The hi setting sounds very 60s, whereas the low is positively doomy.
The crazy mutant artwork was created by Stacey Hine, and is professionally screen printed onto each powder coated enclosure.