This is exactly the problem right here. Konami can't think outside the box more to make unlock events that don't have to fit in with the anime plot timeline. They should just make him unlockable through a bingo mission if it is that hard to come up with a new unlock event with dialogue.
They were clearly just making a joke on the fact he went missing in the GX universe for quite a while...
I feel like Atticus is still one of the most likely remaining GX characters either way, especially since they hinted at Darkness/Nightshroud being a thing, since he had a pretty strong connection to that plot.
This game is super popular, so they will keep adding in lots more characters which is nice. After the DSOD world they also had a survey to request the characters you want to see added.
I did the survey for him. I hope they do what they did last year and give a leaked list of character releases for months in advance. I guess for now we know about Sera and Rex.
However, if they add everything too soon, some duel worlds will run out of characters which is not good. Delaying him would make everything more interesting, I mean... they already gave us Jaden/Yubel I guess we can't really complain.
They're never going to run out of characters. DM has like 10 billion characters already, and I could easily name another half a dozen that would make sense without delving into dumb picks like Zygore or Seeker. It's mostly down to pacing. Obviously if you release a bunch of characters from the same universe at once, people get burned out by it.
Zexal would have enough for at least 7 (Yuma, Astral, Kotori, Shark, Kaito, Cathy, and considering they brought Prana into DL, I won't be surprised to see Cologne)
Arc-V has at least 8 just for Yuya and his clones and Yuzu and her clones
Vrains has at least 7 too (Yusaku, Aoi, Go, Ghost Girl, Revolver, Spectre, and I have no doubt Ai will get in too)
Without mencioning
zexal: tron family, gauche and droite and barians
Arc-v: Reiji and all lancers
Vrains: Soul burner, all ignis and the guy with the drones
Anonymous
not a bad idea
