Sonic the Hedgehog is back in Sonic Mania, a brand-new, retro-themed addition to Sega's storied franchise. Sonic's the fastest gaming mascot around, but his Super Sonic form amps up the speed to 11.

For as long as there have been games there have been fans cracking them open and stuffing new levels inside them - unofficially, of course. For decades modders have been finding ways to sneak extra ...