If being realistic isn't a necessity, my main choice would actually be the
Subrosians (avvy might be a tad spoilerish on that one). Having
Subrosia as a stage would be utterly awesome as well (but second to impossible, however)!
How my inner monolgue about
Subrosians being in SSB is like (I'm not expecting anyone who hasn't played
Oracle of Seasons to really grasp any of the logic of it):
Side Special: Now, this may seem a little iffy and visually crappy, but I'm thinking that the Subrosian would pull off a
Strange Brothers by doing a quick and well-lengthy run towards the desired direction (thinking of it as Fox's Special Side, except slower). The main effect would be to steal the opponent's current weapon if the player in control of the Subrosian manages to hit anyone (and if the opponent is holding any weapon (btw, if the Subrosian performing this attack also would be holding an item, they'd simply be swapped)), and that it of course also would inflict a certain amount of damage.
Special: Throwing
Ore Chunks as projectiles (could be the side special as well). The fact that there are five different types of Ore Chunks in the game fits perfectly; Hard Ore would harm the most, while Fool's Ore would harm the least (perfect, I say).
Down Special: Now, this was a little problematic at first, but my main idea for this is for the Subrosian to, by the help of a shovel, dig up a
Fire Pokey from the ground, which will act as a temporary assistant. This would be a reference to the fact that this is the only area in the game where Fire Pokeys can be met by being dug up.
Up Special: This is something which I'm still having a rather tough time with. My present thought about it is for the Subrosian to teleport through two vortexes and by through that gain a decent third jump substitute (could perhaps even be used to get past a platform which normally would be in the way (by teleporting through it)?). This would anyway be a vague reference to the vortexes in the game which are essential to travel back and forth between Subrosia.
Final Smash: Ugh, I just dunno about this one. A volcano randomly popping up and scatter some devastating rocks here and there, perhaps?
I also idealized the "Masked Young Link" for a while before getting to know how popular that one actually was among internetters. ._. I was so proud of thinking though that one so thoroughly..
(I also made some in-text linking in case anyone would be interested in these awesome creatures :3)