LogFAQs > #923418529

Thinking the possibilities include:
Leon Kennedy/Jill Valentine - Resident Evil has had a good Nintendo history the last almost 20 years now
Dante - Not the best Nintendo history, but he's a big star, and could potentially still make it.
Arthur from Ghosts n Goblins - One of the last remaining iconic NES era platformers, and being Capcom makes his chances better.
Master Chief - If you think Banjo's reveal was big, imagine a Master Chief reveal. Not sure they'll double dip two DLCs into Microsoft though.
Steve from Minecraft - Same as above pretty much.
Ryu Hayabusa - There has been some Tecmo stirrings with Nintendo lately, and he's IMO, the biggest NES era icon who isn't in Smash at this point. I'd be shocked if it happened, but I could also see it. I'm not expecting it this game though.
Tom Nook - The last DLC slot will coincide about with the time of the new Animal Crossing game, so Nintendo could use the last slot for themselves to put in one of the 3 biggest Nintendo exclusions at this point. Not really expecting Nintendo slots in the DLC though, but if any get it, I think he has one of the best shots.
Crash Bandicoot - Not sure if Banjo's inclusion makes him more or less likely. It would seem odd to put a 2nd 64 bit era 3D platformer animal mascot as DLC.
Rayman - Well, he IS already in the ice.
Sans - Undertale has done very well with Nintendo, and this one would make people lose their shit. I could see it happening, but I think it's a low chance.
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Bells, bells, bells!