So upon further analysis, heres what I determined:
It is modified Smash 4's engine and not Brawl. However the official game is very likely going to use a modified Smash 4 engine and should look very close to this, so I'd say this is more in favor of being not fake.
Springman's idle animation appears to be original. No other character hops side to side like that. My first suspicion was Little Mac, but you can tell they are clearly different. Also not a costume for Ryu either. Animations are completely original and pretty faithful to his game.
Next up is Springman's side aerial. Looks like Little Macs right? Its very similar, but appears to be slightly modified. Also the stage seems accurate to the actual stage from Arms
Decidueye doesn't exist on Pokken for Wii U and as far as I know the game hasn't been ripped. That still didn't stop the modding community from making a Decidueye skin on gamebanana. (Springman doesn't exist there).
https://gamebanana.com/skins/159939
Note that Decidueye is pretty different both color, and body structure in from this skin than the supposed leaks.
And its not a direct rip from Sun/Moon either, although the color pallet is more in line.
https://gamebanana.com/requests/7382
Then theres Ice Climbers...and yes they look like a direct Brawl rip, so I don't see much defense for them.
.....
So to sum everything up. Springman has original animations, potentially an original model, and potentially uses Little Mac's side aerial, but I might need a second opinion on that move.
Decidueye's model is not the ones from gamebanana, Sun/Moon or Pokken. Body structure is different, but stance is similar to Pokken. Color pallet matches Sun/Moon and much lighter than Pokken.
Ice Climbers are pretty much from Brawl. But then again so was Wario from brawl into Smash 4 so who knows anymore.