A long time ago, in a meeting far, far away, George Lucas declared that Yoda's species details would remain a secret. Generally, I'm fine with that - it's a big galaxy, and it's nice to have unknown bits. We don't even know the species name. For game designers, this presented certain challenges - how do you stat out Yoda or one of the other two known members of the species?
Turns out, it was a pretty easy answer: treat him (or her) as a Small human.
But what about special species abilities? None listed. All of the obvious things from the movies and stories that make Yoda special (mechanically speaking) are covered by his Jedi abilities, so we're not missing much, if anything, by omitting special species qualities.
I'm not going to add anything mechanically here. Instead, I wanted to point out some roleplaying and story opportunities Yoda's species presents in game play.
Primarily, there is no species backstory, and there isn't likely to be ANY (except whatever George decides to release, if anything). This gives gamemasters and players free reign to include and adapt a major movie-appearing species in their campaigns in a way that won't likely be contradicted by continuity.
The Star Wars universe is filled with unusual species, so the average person isn't going to pay much attention to yet another unusual looking species roaming the galaxy (those species who don't get out much will, but that's another discussion). However, only 3 of Yoda's species have been recorded in history (according to the New Essential Guide to Species), so someone playing the 4th one to be seen (or the second or the first depending on era) ought to attract some attention from someone who KNOWS how rare they are. Especially since all of the known members are not only Force Sensitive, they are Jedi Masters. A new one shows up, people are going to take notice eventually.
So, imagine the story opportunities if an entire party of Yoda's species shows up. Maybe they're Force Sensitive, maybe not. Maybe they're on a specific mission, intending to return to their homeworld/colony/whatever immediately after the task is completed. A GM could treat them much like the Greys of UFO lore, keeping them out of the universe's mainstream consciousness.
Or a gamemaster could take it the opposite way: maybe the FANS don't know about Yoda's species, but perhaps the Universe itself does. Perhaps they aren't special enough to warrant more attention than other species...or maybe they are. The GM could create a homeworld/colony/etc., drop it into the universe, and center a campaign around it. Designing the species history, society, technology and traditions could be very interesting. Speculating on and PLAYING THROUGH the effects of historic galactic events might make for great story-heavy sessions. This would also make a great setting for an alternate universe style campaign.
Of course, a GM can just create their own world and species for similar story options, but by usuing Yoda's species, it brings a new level of interest to many players. Even if a GM doesn't want to go that far, simply using the species as an exercise (like above) can generate ideas for other storylines, characters and ideas.
...hey, what if the player characters discover Yoda's family?
....what if they ARE members of his family?
.....what would the weird relative of Yoda's family be like?
......what if Yoda WAS the weird one?
.......what if the entire species actually is that strong in the Force?
........WHAT DO YOU MEAN YODA HAS AN EVIL TWIN!!!!!!???