My multiverse:
Universe A:
Mario and Luigi were transported to the Mushroom World from Brooklyn, Bowser has seven kids, Yoshi's live in Dinosaur Land and act like ordinary animals, Wario is some evil villain who wants Mario's new castle, Wart is king of Sub-con, Tatanga invades Sara Sara Land for Daisy's affections, and Donkey Kong and Donkey Kong Jr. are old enemies of Mario's.
Universe B:
Mario and Luigi were born in the Mushroom Kingdom, Bowser has Bowser Jr., Yoshi's act a lot more like humans and live on one Yoshi's Island, Wario is a greedy weirdo who opened his own video game company, there is no Wart or Tatanga.
Universe C:
Dr. Mario busts viruses with the help of Nurse Toadstool.
Universe D:
Donkey Kong is the guardian of DK Isles, the son of Cranky Kong, pals around with Diddy and Dixie, and occasionally visits Banjo, Conker, and even the Mario of Universe B.
Other assorted universes:
There might be other universes where Mario is a chef, a demolition worker, a referee, and a archaeologist, as in the cases of Yoshi's Cookie, Wrecking Crew, Punch-Out and Picross.
I'm also trying to figure out what the deal is with Mario vs. Donkey Kong...