You could say the same about Tyranno. True, we don't have his Ace, Ultimate Tyranno, but we have basically everything else aside from Hyper Hammerhead and Volcanic Eruption.
Chumley's unlikely, but look at Tristan or Odion. If they want to release a character, they can easily form a cardpool for them even if all their cards (if any) are already obtainable, or they have too few.
I wouldn't say Odion's "theme" really carried over to his cardpool.
They could easily give Chumley general Beast stuff. (Which they've done in a few video games already.) And Ayer's Rock Sunrise is a solid option for ace card if Master of Oz is a problem. I feel like Chumley would actually be EASIER than Tyranno, assuming only new cards and not re-released cards like Jurassic World.
There's nothing saying it has to be a monster. Blast Held By a Tribute and (kinda) Embodiment of Apophis aren't monsters. They could also just give him a skill that starts him with Master of Oz and her materials like the 5D's characters. I think Ayer's Rock Sunrise makes more sense, though.
(It only just occurred to me, but Master of Oz is female given it has a pouch.)
They could also go for cards he used in the games. Like Des Koala, Vampiric Koala, Nimble Momonga and Frenzied Panda.
Maybe even some newer cards like Wrecker Panda
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Evil Rick
