Guys, you know what feels great?
Bull****ting your way into a victory against a Legend-class Spirit.
I encountered Deoxys (Normal) on the Spirit Board, and faced him with Lucario. Deoxys is a Mewtwo holding a Pokéball, he immediately throws it down and Deoxys himself appears, the stage is Omega Mario Galaxy (I think, it might be Battlefield). I got thrown around a bit until I had ~170% damage, which had filled up my FS Meter, Mewtwo had about 37% damage, I triggered Lucario's Final Smash near the top of the screen, and Mewtwo was directly below me. He took the full brunt of the attack and died.
Unfortunately, I missed the shot to free Deoxys, and didn't have enough SP to take another. So...
I also have a guaranteed Cammy if I can find her (and beat her) on the Spirit Board again; I used all items and somehow missed the shot twice (I'm usually good at Free the Spirit, I swear!).
Finally, don't bother trying to face Rex (Advanced, I think) or Pyra (Legend) if you don't have the ability to render yourself immune to Lava (not just resistant), because Pyra sets the whole stage on fire (unlike most "The Stage is [x]" Spirit Battles, where only the bottom floor is changed), you'll get thrown around unable to do much of anything (except Aerial attacks), while Shulk (Rex) and Lucina (Pyra) whale on you with Fire Bars.