ZachTheNCube,"guessed" these things many things correctly prior:
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Just recently, Zach posted these tweets:
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So Steve and Incineroar will be the last newcomer.
Geno will be DLC in 2019 and will be unlocked for Free if you have Switch Online.
Shadow and Ken are the final Echoes.
It may seem bull (Why is Geno DLC out of all of things?) but his predictions are suprisingly accurate. His prediction matches Verge's sources (Possible Minecraft Rep, 2nd SE Rep, Incineroar, and Ken).
As usual, keep an eye for him...