I was discussing this with a fellow judge yesterday, and we were having some disagreements about how MTR 4.2 applies to a few different scenarios where a player does a bunch of activations of something all at once. At issue, in particular, is this bullet point from MTR 4.2:

• Whenever a player adds an object to the stack, he or she is assumed to be passing priority unless he or she explicitly announces that he or she intends to retain it. If he or she adds a group of objects to the stack without explicitly retaining priority and a player wishes to take an action at a point in the middle, the actions should be reversed up to that point.
  

The scenarios, then:
1. I control a Scavenging Ooze. I attack, and you choose not to block. I tap 2 Forests and activate 2 times, targeting the 2 creatures in your graveyard. You say, "In response, Lightning Bolt it."
2. I cast Lightning Storm and plop 25 lands down (which I had previously drawn from Ad Nauseam) to charge up the Storm. You pay 2 life and say, "Redirect to Spellskite.“
3. I cast Lightning Storm and plop 10 lands down. You say, ”Redirect to Spellskite.“ I plop another land down. You plop a land down.

I'm confused, because I might be misremembering an old version of this section, or maybe misremembering a wording that never existed, or extrapolating from something else entirely. I was under the impression that if I activate something a bunch of times, that I'm intending that they're all going to go on the stack and resolve individually, not go on the stack all at once (unless I explicitly retain priority). So if I activate my Ooze several times, and you want to respond ”somewhere", we have to rewind through some number of activations–and implied resolutions–of the ability. … Right?

That last part is the part I'm having a hard time coming to terms with. Does MTR 4.2 (or anything else) say anything about whether or not these activations all resolve or not in some kind of implied/automatic fashion? In each case, what does the stack look like?

Edited Jack Hesse (Oct. 19, 2015 05:28:44 PM)

You are correct, I believe, in your interpretation. The philosophy behind this is so that a player doesn't have to explicitly call out the individual activation and resolution of each of these to not get blown out (take a shade with B: +1/+1 until eot vs Direct Damage).

For clarity's sake I am going to use AP for “I” and NAP for “you”

Scenario 1; 4.2 says the stacking of abilities by the AP is done so they are activating, resolving, then activating again. NAP can interrupt this sequence at either point - with the 1st ability on the stack, or with the 1st ability resolved and the 2nd on the stack.

Scneario 2; Again, NAP can interrupt the “chain” at any point they choose. Assuming they understand what they're doing, they wait until all 25 individual activations have resolved, then activate their Spellskite. If they interrupt the chain at a given earlier point (for some unknown reason) then however many lands are returned to hand, and AP can continue to activate.

Scenario 3: This feels messy, like the players haven't necessarily communicated completely, but to me it looks as if:
The 10 activations have resolved.
NAP has activated skite, that ability has resolved.
AP has activated Storm, that ability has resolved.
NAP has activated Storm, (presumably with the ability about to resolve)

This one would require investigation as to where/what the players think has happened. I hope they agree.

You aren't misremebering. The way the shortcut is worded, you are assumed to be passing priority after each ability goes on the stack. This is the same as trying to let each resolve individually. In robot magic, if you pass priority and opponent passes back, the ability resolves and you get to do more after, like activate it again. If your opponent wants to respond at that point you get to decide what to do based on that.

Situation #1 - ask when player wanted to cast the bolt. Only 1 ability at most will be on the stack.
Situation #2 - ask when player wants to use spellskite, likely he will want to use after all the lands are out of your hand.
Situation #3 - you get to play “who gets last redirect” game as you and spellskit keep changing target back and forth.