Third, take stuff from MM as a whole. Maybe throw deku nuts, maybe bombchus (honestly they should be an item, now that I think about it), maybe use Deku Link's flower propellers for his Up B. There's plenty for them to use; they've worked with far less.
I'd love to see some nods to Link's many forms from MM. To me, they were partially what made MM have the most fun gameplay in the series, and I'd be thrilled if Skull Kid made some references to the likes of Deku Link, Zora Link, and Goron Link (or even Fierce Deity Link). He should probably mainly use Majora moves, but seeing the Deku flowers for a jump move or a Zora-style energy field could work very well. Also, since he's somewhat in charge of Tael the fairy, maybe he could send him out to give opponents a light smack for some A attacks.
And then there's the little things, like taunts and victory stances, which pretty much write themselves. Laughing like a crazed child, dancing like a puppet, playing an ocarina really badly, etc.
Also, I'm with JezMM in that I just don't like Skyward Sword that much. It had its moments, but I didn't find much of it to be as enjoyable as pretty much any of the other Zelda games. Ghirahim has personality, but he really isn't very unique. I never felt like what he was saying held that much weight. "Oh, yep, you're gonna kill me slowly and painfully, mm-hmm. Can we skip this speech and get to the part where I kick your ass and you run away?"