Super Smash Brothers Ultimate - 108 stages according to Corocoro

But yeah, this is definitely a leak I can get behind. Mainly because it's a photograph of physical media, of which it's Corocoro, one of the more reliable source of information with countless Pokemon and other things to validate its reputation.
108 is, funnily enough, an important number in Buddhism and Japan. With Buddhism, it refers to the six senses; multiplied by the three emotions of neutrality, pain, and/or pleasure; multiplied by internal or external happenings; ending with whether the event happened in the past, present, or future. In Japan, it refers to the act of Buddhist temples ringing the bell 108 times, casting out the old year and bringing in the new year.

This is interesting, given Sakurai's previous fixation on 103.

It makes sense, though; there's six open slots on the stage select screen. Five more stages would fill up all but one slot, which would be reserved for a "next page" button to access DLC stages and/or custom stages.