AdmiralMemo wrote:If a token gets Undying and doesn't have a +1/+1 counter on it, it still doesn't come back due to SBAs eliminating it once it hits the graveyard, right? I'm assuming the Undying trigger still goes on the stack, but fizzles due to having no target.
Also, if a non-token creature somehow has both Undying and Persist, I'm assuming it just infinitely recycles from the graveyard due to the counters canceling each other out.
If that's true, Undying + Persist = Poor-man's Indestructible, with bonus Dying and ETB triggers if other creatures care about that. I'm thinking some fun could be had with Puppeteer Clique while Mikaeus, the Unhallowed is on the battlefield. Alternatively with Mikaeus, Murderous Redcap becomes the best blocker, with bonus Shocks. Aerie Ouphes just wipes out any opponent's fliers with no draw-back. With a sac outlet, Woodfall Primus becomes a wiper of lands, artifacts, and enchantments.
I'm not a judge but the combination of Persist and Undying does let you keep bringing creatures that have both those traits back again and again forever (until they lose one or the other ability). You could also use persist creatures and Melira, Sylvok Outcast to get the same result, as she just outright stops the -1 counter that Persist would place on the returning creature from ever happening for as long as she's in play, and Cauldron of Souls + Mikaeus will let you bring any non-human back over and over again (albeit not infinitely by itself like Persist creatures + Mikaeus and a sac outlet allow, as you have to tap the Cauldron).
As for tokens, if they have Persist/Undying or there's some other on-board mechanic like Athreos that triggers when they die, those things all still happen, but there's nothing to bring back to the battlefield/hand/etc because once a token leaves the battlefield it stops existing; Persist/Undying trigger when a creature hits the yard, which both token and real creatures do, and then the triggered ability checks whether that creature is still in the yard when it tries to resolve - the regular creature (normally) will be, the token by definition can't exist there so the effect will always fizzle, as you correctly surmised. The requirement for the object to still be in the graveyard as the trigger resolves is also why cards like Relic of Progenitus and Nihil Spellbomb are not your friends if you're playing the Persist/Undying shenanigans deck, as your opponent could wipe the board and then exile your graveyard with the triggers on the stack.
On a somewhat related note, if an Undying creature with existing +1/+1 counters on it dies in combat to a creature with Wither/Infect (ie, dies to having -1/-1 counters placed on it), it doesn't come back because it's already been sent to the graveyard before the game gets around to canceling out the +1/+1 counters; it if had survived combat then Undying would be good to go, but since the card as it last existed on the battlefield had a +1/+ counter, Undying won't trigger thanks to that intervening if clause.