This guy on tapped out came up with some combo, which is the following: Psionic Sliver, Blur Sliver, Everlasting Torment, and Mikaeus, the Unhallowed. You tap the psionic sliver for the three damage to your opponent's face, then it dies due to -1/-1 counters. He thought that the +1/+1 from undying would be canceled with one of the -1/-1 counters, so undying would trigger again, and again, and again... until you have burned you opponents to death.
I personally think that +1/+1 counters aren't canceled by -1/-1 counters, and would like to know if this is true.
While +1/+1 counters and -1/-1 counters are indeed removed in pairs of a +1/+1 and -1/-1 as a state-based action (C.R. 704.5q), this won't make the undying ability of a creature trigger if that creature with a +1/+1 and -1/-1 counter dies at that moment. This is because in this case, those counters are removed this way and the creature dies simultaneously (C.R. 704.5f, 704.5q, 704.3), meaning it would have a +1/+1 counter at the last moment it was on the battlefield; thus the undying ability won't trigger (C.R. 603.4). (Note that leaves-the-battlefield abilities, such as undying [C.R. 702.93a, 603.6c], check the state of the game from just before the permanent leaves the battlefield, not after [C.R. 603.10a, 603.10; see also C.R. 704.7 for this case especially].)
But note that Psionic Sliver deals only 2 damage, not 3, to the targeted creature or player when its ability resolves, regardless of its power, and that the effect of Mikaeus's last ability gives certain creatures +1/+1 (C.R. 613.4c), which is not the same as putting a +1/+1 counter on those creatures (C.R. 613.4d).
EDIT (Sep. 28): One rule was renumbered with Ixalan.
EDIT (Dec. 23, 2022): Edited, including to conform to rule changes in the meantime.
It is true that +1/+1 and -1/-1 counters annihilate each other as a state-based action, BUT the combo still doesn't work, because Psionic Sliver dying from having 0 toughness is also a state-based action. Stated-based actions that are applicable at the same time, happen at the same time, which means that at the last moment it was on the battlefield, Psionic Sliver did still have a +1/+1 counter on it. It's a 0/0 on the battlefield with a +1/+1 counter and 3 -1/-1 counters, and then it's in the graveyard. Undying looks at what it had at it last existed on the battlefield to know if it should trigger, so it doesn't.
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I'm a former judge (lapsed), who keeps up to date on rules and policy. Keep in mind that judges' answers aren't necessarily more valid than those of people who aren't judges; what matters is we can quote the rules to back up our answers. When in doubt, ask for such quotes.
It is true that +1/+1 and -1/-1 counters annihilate each other as a state-based action, BUT the combo still doesn't work, because Psionic Sliver dying from having 0 toughness is also a state-based action. Stated-based actions that are applicable at the same time, happen at the same time, which means that at the last moment it was on the battlefield, Psionic Sliver did still have a +1/+1 counter on it. It's a 0/0 on the battlefield with a +1/+1 counter and 3 -1/-1 counters, and then it's in the graveyard. Undying looks at what it had at it last existed on the battlefield to know if it should trigger, so it doesn't.
You're missing the fact that none of the four cards mentioned says to put a +1/+1 counter on anything (Mikaeus, for example, gives certain creatures +1/+1, which is not the same).
EDIT (after comment 6 was posted): With the exception of the undying ability granted by Mikaeus, which I missed.
EDIT (Jan. 5): Edited preceding edit note for clarity.
The real issue is that Psionic Sliver is a 4/4 due to 2/2 +1/+1 from Mike and +1/+1 from the undying counter. So this combo deals 4 damage per sliver per turn and does work sort of. If there is Night of Souls' betrayal on the battlefield then the previous answers are correct.
It is true that +1/+1 and -1/-1 counters annihilate each other as a state-based action, BUT the combo still doesn't work, because Psionic Sliver dying from having 0 toughness is also a state-based action. Stated-based actions that are applicable at the same time, happen at the same time, which means that at the last moment it was on the battlefield, Psionic Sliver did still have a +1/+1 counter on it. It's a 0/0 on the battlefield with a +1/+1 counter and 3 -1/-1 counters, and then it's in the graveyard. Undying looks at what it had at it last existed on the battlefield to know if it should trigger, so it doesn't.
You're missing the fact that none of the four cards mentioned says to put a +1/+1 counter on anything (Mikaeus, for example, gives certain creatures +1/+1, which is not the same).
I meant the +1/+1 counter that it would get from undying. It's a 3/3, it deals 2 damage to a target and 3 to itself, it dies, it comes back with a +1/+1 counter. I omitted to describe that process and jumped to the point after that part is done for my explanation. But anyway, as snarfblattcheesewizard said,
The real issue is that Psionic Sliver is a 4/4 due to 2/2 +1/+1 from Mike and +1/+1 from the undying counter.
Except that with the four cards mentioned, the combo still doesn't really work. You could activate the Psionic ability that Blur Sliver has to have it "finish off" Psionic Sliver, having it coming back with Undying, but that's not enough to generate a productive loop, because Blur Sliver will not be able to "undie" more than once, it will die with a +1/+1 on it if you activate the Psionic ability on it without first removing the +1/+1 counter on it. You could make a loop of the Slivers dying and coming back by having them target each other, but you're not accomplishing anything without yet another card involved.
I'm a former judge (lapsed), who keeps up to date on rules and policy. Keep in mind that judges' answers aren't necessarily more valid than those of people who aren't judges; what matters is we can quote the rules to back up our answers. When in doubt, ask for such quotes.
No. A 1/1 sliver will be a 2/2 with Mikaeus out, and become a 3/3 when undying. If you activate the ability granted by Psyonic Sliver with Everlasting Torment on the field, after it resolves, the sliver will be a 0/0 creature, with both a +1/+1 counter and three -1/-1 counters. State based actions will then simultaneously annihilate the +1/+1 counter with a -1/-1 counter and sent it to the graveyard. Leaves-the-battlefield triggers, like undying, trigger on the appearance of the permanent right before it went to the graveyard, and at that time, the creature had a +1/+1 counter on it, so undying is shut off and won't trigger.
Psionic Sliver, Blur Sliver, Everlasting Torment, and Mikaeus, the Unhallowed. You tap the psionic sliver for the three damage to your opponent's face, then it dies due to -1/-1 counters. He thought that the +1/+1 from undying would be canceled with one of the -1/-1 counters, so undying would trigger again, and again, and again... until you have burned you opponents to death.
I personally think that +1/+1 counters aren't canceled by -1/-1 counters, and would like to know if this is true.
BChainer Sac-Based ControlB
UWOjutai Control/VoltronWU
But note that Psionic Sliver deals only 2 damage, not 3, to the targeted creature or player when its ability resolves, regardless of its power, and that the effect of Mikaeus's last ability gives certain creatures +1/+1 (C.R. 613.4c), which is not the same as putting a +1/+1 counter on those creatures (C.R. 613.4d).
EDIT (Sep. 28): One rule was renumbered with Ixalan.
EDIT (Dec. 23, 2022): Edited, including to conform to rule changes in the meantime.
You're missing the fact that none of the four cards mentioned says to put a +1/+1 counter on anything (Mikaeus, for example, gives certain creatures +1/+1, which is not the same).
EDIT (after comment 6 was posted): With the exception of the undying ability granted by Mikaeus, which I missed.
EDIT (Jan. 5): Edited preceding edit note for clarity.
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