Each of the tokens created by Redoubled Stormsinger's last ability copies the original characteristics of the token it's copying as stated by the effect that created that token
At the beginning of the next end step, sacrifice it
I'm out of the loop, but my friend had a nasty deck years ago with Phyrexian Obliterator, though it doesn't necessarily add value beyond itself like some of your other choices (Dauthi Voidwalker looks wild)

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It's an incredible pump effect, and because it's attached to a creature and not an Instant or Sorcery, you can find it using green's excellent tutor effects