The Stack

This is a place holder for a discussion about the stack and it's function in the game.

For now, just know that it is where spells and abilities sit and wait to resolve or "go off".  Things resolve "First in, Last out".  That means the last thing put on the stack will happen first.

So say during combat my goblin arsonist dies along with one of their creatures they also have an unruly mob.  What happens first?  Can the goblin arsonist ping the mob before it gets a counter

At first I was thinking they happen simultaneously but these abilities would have to use the stack also wouldnt they?  If so I get priority meaning his resolves first?

So, when a bunch of things would happen or trigger simultaneously, they get placed on the stack by players in APNAP order (active player - non-active player).  And as Poof said, the last person to put their triggers on the stack will have theirs resolve first.

Poor arsonist

So if the same situation happened during his combat phase my goblin arsonist would be able to kill off the mob

I dont think so because active player, you, first, then opponent. Opponents thing happened last. Mob is 2/2 before you can shock for 1. 

Sit. 1) Your attack.

You attack with Goblin Arsonist.
Your opponent has an Unruly Mob and a 1/1 Human token.  They block the arsonist with their token.

When the combat damage dealt kills both the human token and the arsonist, two triggers are going to wait to be put on the stack.  The first time for that will be at the beginning of the End of Combat Step.

Since you were attacking, you are the Active player and you put your triggers (the one point of damage from the arsonist) on first.  Then you opponent will put their Mob's trigger on the stack.  Now Players would get a chance to respond with instants and abilities.  If no one does, the mob will get a counter and the arsonist will deal its damage.

Sit 2) Your Block

Your opponent has an Unruly Mob and a 1/1 Human token.  They attack with their token.
You block the token with Goblin Arsonist.

Your opponent will put the mob's trigger on the stack, and then you will put the arsonist's damage on the stack.  The last one on the stack will happen first, so the damage will be deal to the mob. then the mob will die before the +1/+1 trigger will resolve.

Ah this helps my understanding of the stack I was found it confusing thanks blackjester

An important thing to remember is that each player receives and must pass priority for each thing to resolve off the stack.  The stack doesn't just resolve all at once, you can chose to let the top item or two resolve on the stack, but then respond to the third item.

One time opponent had rot wolf attacked I declared no blockers because I had none he then used I think 3 mutagenic growths and would have killed me but in response I used dismember.  His rot wolf died but he did not believe me.  I almost pulled the trigger and dismembered after he declared it as an attacker but that would have cost me the game he would have kept it alive in response with his mutagenic growths

Other tricky situations arise when a creatures with abilities leave the battlefield.  During prerelease I tap beguiler of wills to take his creature he used something like vapor snag to send it back my hand I told him I still take over his creature because the ability is still on the stack and is going to resolve he and the group next to us said I was wrong until I called the judge over to
Clarify

Let's say I have priority and cast a spell now my opponent has priority and cast a spell or as many he wants before priority is given back to me right?  I can't interrupt one of his spells if he was still going to cast another? So when hes done priority returns to me and I have nothing to play.  Does he get priority back and have to pass before anything resolves?  After the first spell resolves off the top I get priority then him before the next spell resolves?

One time opponent had rot wolf attacked I declared no blockers because I had none he then used I think 3 mutagenic growths and would have killed me but in response I used dismember.  His rot wolf died but he did not believe me.  I almost pulled the trigger and dismembered after he declared it as an attacker but that would have cost me the game he would have kept it alive in response with his mutagenic growths

The assumption is that he cast each one in response to the first. Your ability to play Dismember is because your opponent didnt specify that he was letting each one resolve before casting the next.