Rule savvy peeps needed:

[Jdogtoocool]

Ok so my opponent and I both are at 2 life, he has a tapped {Geralf's Messenger} and I just put down {Massacre Wurm}, who loses the 2 life first?

[TBNL]

Ok so my opponent and I both are at 2 life, he has a tapped {Geralf's Messenger} and I just put down {Massacre Wurm}, who loses the 2 life first?

He would. The Wurm's ability triggers when the Messenger hits the graveyard. The Messenger's ability triggers once it returns to the battlefield. So it has to die before it can come back.

I believe that is correct. Unless there's something overly complex with the Stack involved.

[Tetsomori]

The wurms trigger goes on the stack as does undying but the active player chooses the stack order if im not mistaken (active player is whomevers turn it is)

[MasteroftheCraft]

Whichever abilty activates first, is the "winner". Then the opposind ability is triggered. I believe thats correct.

[TBNL]

So if you chose to put the Undying trigger on the Stack first, you win. Massacre Wurm first, you lose

[BlackJester]

The non-active player lives.

The active player will put their "kill the opponent" trigger on the stack first, followed by the next player.  The non-active player's trigger will resolve before the active player's trigger.

In your example, its probably your turn if you cast the wurm, so the messenger dies.  This action will cause two triggers, undying and wurm's lose two life.  Since the triggers are owned by different players, the will get put on in order of APNAP (active player, non-active player).  You put yours on, they put theirs.

Undying resolves, bringing back messenger and putting its trigger on the stack while the wurm's is still waiting to resolve.

[Sagemaster]

Same situation but messenger is untapped, and opponent (at 2 life) swings for lethal I block with messenger who wins?

[BlackJester]

Same situation but messenger is untapped, and opponent (at 2 life) swings for lethal I block with messenger who wins?

Very similar, they are the active player, you would win for the same reasons as before.  Two triggers from different players, APNAP.  You trigger goes on last, resolves first.

[Sagemaster]

So the messenger would win me the game?

[BlackJester]

So the messenger would win me the game?

Unless they had other attackers dealing lethal, of the attacking creature had lethal trample.  In that case, all combat damage is dealt at the same time.  If you survive combat damage, your messenger would kill your opponent before wurm's ability kills you.

[TBNL]

So the messenger would win me the game?

Unless they had other attackers dealing lethal, of the attacking creature had lethal trample.  In that case, all combat damage is dealt at the same time.  If you survive combat damage, your messenger would kill your opponent before wurm's ability kills you.

Interesting. APNAP, I'll have to remember that

[Poof]

You can't choose the stack order of an item you don't control.

[Jdogtoocool]

Wait so does my wurms ability win me the game or not? (it's my turn)

[MasteroftheCraft]

Wait so does my wurms ability win me the game or not? (it's my turn)

They appear to be saying "NO"

[Poof]

You lose your stuff goes on the stack first since it's your turn meaning his stuff goes on the stack on top of yours and happens first.