1) Will both the Ogre Slumlord and Nightmare Shepherd death-triggered abilities resolve successfully? Additionally, will the Desecrated Tomb's triggered ability resolve successfully?
From the Gatherer Rulings for Nightmare Shepherd: "The token copies the creature as it last existed on the battlefield before it died, not as it existed in the graveyard before it was exiled." This indicates the creature in question would die and actually make it to the graveyard, THEN be exiled, allowing any "when a creature dies" effects to trigger prior to the exile and subsequent copy generation, and "when a card leaves your graveyard" effects to trigger off the exile itself, correct?
2) When does the decision to exile or not (the Shepherd's triggered ability is a MAY on the exile) occur?
In particular, if a player wants to respond to the Shepherd's triggered ability going on the stack, has the decision to exile already been made, or do you decide after the response (and maybe change your mind)? Alternatively/additionally, would another player known your decision before or after they would need to respond to the ability, and could a response prevent the exile from occurring (perhaps by exiling the yard before the Shepherd could exile it)?
3) When does the Marrow-Gnawer's ability go on the stack as compared to the Orge's/Shepherd's?
As the creature death (sacrifice) is part of the cost of the Marrow-Gnawer's ability, does that ability go on top of the other two, below the other two, or do the three get put on the stack at the same time (and thus can be ordered however the controller wishes)?
4) How may rats does the Marrow-Gnaer's ability see when determining the number of tokens to create?
This partially depends on the answer to #3. In a best-case scenario, the Orge has already created a rat token and the Shepherd has already created a 1/1 Nightmare Marrow-Gnawer, so the ability sees and creates 2 rats - does it?
5) In an EDH game with Marrow-Gnawer as the commander, could the Marrow-Gnawer go the yard, then return to the command zone via the Shepherd's exile? If yes, would the Shepherd's ability resolve successfully (does it care if the Marrow-Gnawer actually went to the exile zone?)?
1. Triggered abilities in general don't necessarily "resolve successfully"; in general, a triggered ability resolves only if all players pass while that ability is on the top of the stack (C.R. 117.4). See the example scenario below.
2. The appropriate player chooses whether—
to create a Rat token with Ogre Slumlord's ability, or
to exile the card referred to by Nightmare Shepherd's ability,
as the case may be, when the corresponding ability resolves, not when it triggers or goes on the stack (C.R. 608.2d, 603.5). Other players can "respond" to the ability, but they have to do so without knowing what choice the appropriate player will make this way. In general, if that player makes such a choice in advance, they will be bound to that choice unless another player intervenes (C.R. 722.2a-c; for sanctioned tournaments, see M.T.R. 4.2). See also this thread.
3. As a player activates Marrow-Gnawer's activated ability, they put that ability on the stack before they pay its costs (C.R. 602.2a-b, 601.2h). Any ability that triggers as that player pays the cost of that ability (e.g., as they sacrifice Marrow-Gnawer) will go on the stack above that activated ability and get to resolve before it (C.R. 405.2, 117.4). See also this thread.
4. Marrow-Gnawer's activated ability cares about the number of Rats "you control" when the ability resolves, which is not necessarily the number of Rats "you control[led]" when the ability was activated (C.R. 608.2g).
5. If the choice is made to exile the card referred to by Nightmare Shepherd's triggered ability, a token is still created even if that card is a commander and is moved to the command zone instead of to exile (under C.R. 903.9)created. This is because the form "You may exile it. If you do, ..." expresses a cost which is still paid even if the actions involved in paying it are replaced with something else (C.R. 118.11, 118.12; see also this thread)(C.R. 118.12). Note, however, that the token created this way won't count as a commander (C.R. 903.3, 706.2); thus, for example, any combat damage dealt by that token won't count as combat damage dealt by a commander for the purposes of C.R. 903.10a. See also this thread.
Take the following scenario:
Assume you control Nightmare Shepherd, Ogre Slumlord, Desecrated Tomb, and Marrow-Gnawer. Also assume that Marrow-Gnawer isn't a token.
You activate Marrow-Gnawer's activated ability and tap and sacrifice Marrow-Gnawer to pay for that ability. Nightmare Shepherd's and Ogre Slumlord's triggered abilities trigger. They go on the stack in the order of your choice. Assume you choose to order the former on top of the latter.
All players pass, then the Nightmare Shepherd ability resolves. You choose to exile Marrow-Gnawer (making Desecrated Tomb's ability trigger) and so create a token that's a copy of Marrow-Gnawer as it existed at the last moment it was on the battlefield (which is what "that creature" on that ability refers to), with certain exceptions (C.R. 608.2g, 113.7a, 109.2; compare Nightmare Shepherd with God-Pharaoh's Gift or Séance; with respect to the "it" in the ability's "you may exile it", see also this thread). The ability leaves the stack, then you put the Desecrated Tomb ability on the stack.
All players pass, then the Desecrated Tomb ability resolves. You create a Bat token, then the ability leaves the stack.
All players pass, then the Ogre Slumlord ability resolves. You choose to create a Rat token, then the ability leaves the stack.
All players pass, then the Marrow-Gnawer ability resolves. You now count the number of Rats you control (which includes the Rat token you just created due to the Ogre Slumlord ability and the Marrow-Gnawer token created due to the Nightmare Shepherd ability) and create that many Rat tokens. The ability leaves the stack.
EDIT (Jul. 2, 2020): Edited to conform to rule update with Core Set 2021; the rules changed so that a commander that's exiled doesn't necessarily go to the command zone immediately.
EDIT (Jul. 22): Reinstate one rule citation.
EDIT (Jun. 26, 2021): Edited, including because one rule was renumbered in the meantime.
1) Will both the Ogre Slumlord and Nightmare Shepherd death-triggered abilities resolve successfully? Additionally, will the Desecrated Tomb's triggered ability resolve successfully?
From the Gatherer Rulings for Nightmare Shepherd: "The token copies the creature as it last existed on the battlefield before it died, not as it existed in the graveyard before it was exiled." This indicates the creature in question would die and actually make it to the graveyard, THEN be exiled, allowing any "when a creature dies" effects to trigger prior to the exile and subsequent copy generation, and "when a card leaves your graveyard" effects to trigger off the exile itself, correct?
2) When does the decision to exile or not (the Shepherd's triggered ability is a MAY on the exile) occur?
In particular, if a player wants to respond to the Shepherd's triggered ability going on the stack, has the decision to exile already been made, or do you decide after the response (and maybe change your mind)? Alternatively/additionally, would another player known your decision before or after they would need to respond to the ability, and could a response prevent the exile from occurring (perhaps by exiling the yard before the Shepherd could exile it)?
3) When does the Marrow-Gnawer's ability go on the stack as compared to the Orge's/Shepherd's?
As the creature death (sacrifice) is part of the cost of the Marrow-Gnawer's ability, does that ability go on top of the other two, below the other two, or do the three get put on the stack at the same time (and thus can be ordered however the controller wishes)?
4) How may rats does the Marrow-Gnaer's ability see when determining the number of tokens to create?
This partially depends on the answer to #3. In a best-case scenario, the Orge has already created a rat token and the Shepherd has already created a 1/1 Nightmare Marrow-Gnawer, so the ability sees and creates 2 rats - does it?
5) In an EDH game with Marrow-Gnawer as the commander, could the Marrow-Gnawer go the yard, then return to the command zone via the Shepherd's exile? If yes, would the Shepherd's ability resolve successfully (does it care if the Marrow-Gnawer actually went to the exile zone?)?
Thanks in advance!
2. The appropriate player chooses whether—
3. As a player activates Marrow-Gnawer's activated ability, they put that ability on the stack before they pay its costs (C.R. 602.2a-b, 601.2h). Any ability that triggers as that player pays the cost of that ability (e.g., as they sacrifice Marrow-Gnawer) will go on the stack above that activated ability and get to resolve before it (C.R. 405.2, 117.4). See also this thread.
4. Marrow-Gnawer's activated ability cares about the number of Rats "you control" when the ability resolves, which is not necessarily the number of Rats "you control[led]" when the ability was activated (C.R. 608.2g).
5. If the choice is made to exile the card referred to by Nightmare Shepherd's triggered ability, a token is
still created even if that card is a commander and is moved to the command zone instead of to exile (under C.R. 903.9)created. This is because the form "You may exile it. If you do, ..." expresses a costwhich is still paid even if the actions involved in paying it are replaced with something else (C.R. 118.11, 118.12; see also this thread)(C.R. 118.12). Note, however, that the token created this way won't count as a commander (C.R. 903.3, 706.2); thus, for example, any combat damage dealt by that token won't count as combat damage dealt by a commander for the purposes of C.R. 903.10a. See also this thread.Take the following scenario:
EDIT (Jul. 2, 2020): Edited to conform to rule update with Core Set 2021; the rules changed so that a commander that's exiled doesn't necessarily go to the command zone immediately.
EDIT (Jul. 22): Reinstate one rule citation.
EDIT (Jun. 26, 2021): Edited, including because one rule was renumbered in the meantime.