Q:Two questions: If I summoned a Gravetiller Wurm, then my opponent responded with Smite The Monstrous on it and then I responded with Undying Evil, would my Undying Evil resolve first and bring back my Wurm? and If it did would it come back with the 1 +1/+1 counter from the Undying Evil and the 4 +1/+1 counters from it's Morbid ability?
Quick note, remember that Gravetiller Wurm has to actually enter the battlefield (resolve) before they can target it with Smite the Monstrous. Can’t kill what hasn’t appeared yet, right?
Remember that the stack resolves in “last in, first out” order. That is to say, the last spell cast/ability is the first to resolve.
Here’s a detailed answer. Currently the stack looks like this:
Undying Evil resolves, giving your creature Undying. Then Smite the Monstrous resolves, killing your Wurm. The Undying your creature has now triggers from the graveyard, bringing it back on the battlefield. Since your creature did indeed die, it enters the battlefield with morbid, gaining four +1/+1 counters on it. So it’ll have one +1/+1 counter from Undying, and four +1/+1 counters from Morbid.
Grats, you made a very nice play.