The way they capitalize Superb kind of makes it sound like it might be one of the "super" character roaming events. Either way, I have no idea who that could be. Late March: Jesse! Yay!
i didn't write unlockable... i wrote "they will release" so there are coming new chars to Duel Links. And i don't think they will make only Character Events in GX...
Of the duelists we know are coming, yeah, Sartorius makes the most sense. Maybe with a slim chance of Atticus. (Though I suspect they'd have either played up the performance aspect or Nightshroud influence for Atticus.)
The new skill is obviously something Dragon-focused, since the new Structure Deck is a Dragon one. (Also ties in with the Dragon focus of the recent Chazz-a-Thon.) Maybe one that sends Dragons to the Graveyard somehow? Or yet another high-level support skill...
I hope it’s Bakura, Tristan, or Marik. Mostly Bakura, it seems he would say this unless it’s Syrus. Regular Bakura would probably have Change of Heart as his signature card. He could be the first to have a spell as his Signature Card.