I have no undertale experience so I don't even know if Asriel has one, but I'm not a strict follower of canon/lore as my World of Warcraft worgen characters have tails while the in game models of worgen don't. But it felt so weird having such a canid creature that Didn't have a tail. So I broke away from canon for Volta and Plothole. (plot's another lore fracture but one condoned in game. Worgen came AFTER WotLK, where death knights were made, used, liberated, and killed. Why allow worgen DK? Or Pandaren DKs for that matter but apparently that's gonna be a thing next xpac... bliz, u cray cray.)
TBH I'm good either way, but I couldn't decide, especially since I already drew him without one in Curiousity XD
I don't think he does. I'll have to replay the game and see what his overworld sprite looks like facing sideways since it's surprisingly difficult to find online. The good thing about Undertale though is that it's specific enough to make you fall in love with the characters, but also there's not a large amount of solid back story. You a few get plot necessary things, but other than that fans can pretty much do what they want. Then you got things like Gaster, who are hinted at and may only be seen in game if you're lucky enough to start the game with a particular "Fun Value"
Well, why not XD Also, Blizzard are crazy anyway XD