In your scenario, the blocking creature must be assigned an amount of damage greater than lethal damage (and other conditions must be met) for Aegar's ability to trigger for that creature.
For purposes of Aegar, a permanent was dealt "excess damage" if "one or more sources ... together dealt"—
"an amount of damage to [the] creature greater than lethal damage", or
"an amount of damage to [the] planeswalker greater than that planeswalker's loyalty before the damage was dealt",
as the case may be (C.R. 120.10). The trample ability, however, changes how combat damage is assigned, not how it's dealt (review C.R. 702.19).
The restriction "This ability triggers only once each turn" applies only to the triggered ability where that restriction appears. It doesn't apply to other triggered abilities, even if they have the same text as that ability. See also C.R. 113.2c. (A similar principle applies to activated abilities that say "Activate only once each turn"; see also this thread.)
The day-and-night mechanic is separate from the abilities—
"At the beginning of each upkeep, if no spells were cast last turn, transform [this permanent]", and
"At the beginning of each upkeep, if a player cast two or more spells last turn, transform [this permanent]".
The mechanics article, though, didn't state whether transforming double-faced cards with either ability will replace that ability with daybound or nightbound, respectively. Thus, it can be presumed that those cards won't change in this respect with the upcoming set.
To be clear, ninjutsu is an activated ability which uses the stack (C.R. 702.49a, 602.1, 602.2). However, many of the same principles apply to Sakashima's Student entering the battlefield via ninjutsu as they do to Sakashima's Student resolving.
For example, players don't have priority to cast spells while an ability is resolving (C.R. 117.2e, 117.1a), so that my comment 2's second sentence applies accordingly to Sakashima's Student entering via ninjutsu or resolving as it does to Clone resolving. It likewise applies accordingly to Clone or Sakashima's Student entering the battlefield due to Aether Vial.
In general, while a spell such as Clone is resolving, players don't have priority to cast spells or activate abilities (C.R. 117.2e, 117.1a-b). Thus, for example, after you decide that Clone will be a copy of a creature and announce which creature, players can't cast spells in an attempt to stop Clone from being a copy of that creature (or even from entering the battlefield); rather, by the time a player gets priority again, Clone will have already entered the battlefield (C.R. 608.3, 117.3b).
Once your upkeep begins, the triggered ability on Vesuvan Doppelganger will trigger, and then go on the stack, when you can target Triskelion; this happens before any player gets priority to activate abilities, such as Triskelion's second ability (C.R. 108.1, 117.5, 603.3d, 601.2c, 117.1b; C.R. 503.1, especially C.R. 503.1a).
The triggered ability on Vesuvan Doppelganger targets a "creature" according to its Oracle text (C.R. 108.1, 115.1d). Thus, if that creature becomes illegal, the ability will fail to resolve (C.R. 608.2b).
You may be confused because of the presence of X on Curious Herd.
In this sense, compare Curious Herd (and Dockside Extortionist and Alibou, Ancient Witness) with Archipelagore or Custodi Soulcaller, which both have abilities that contain an X that has to set in order for targets to be chosen (C.R. 603.3d, 601.2b; see also C.R. 107.3e). In contrast, Dockside Extortionist's ability doesn't require setting X as the ability goes on the stack (review C.R. 603.3c-d, 601.2). See also Necrologia, which requires you to choose an X in order to pay its additional cost (C.R. 601.2b, 601.2f, 108.1).
Yes. Because of Enchanted Evening, Archon of Sun's Grace will be an enchantment at the first moment it's on the battlefield, so its last ability will trigger (C.R. 603.6a-b). See also this thread.
Yes; Mark of the Oni's ability "You control enchanted creature" is a static ability that works only while Mark of the Oni is on the battlefield and attached to something (C.R. 611.3b, 113.6, 303.4m, 604.1).
So the copies can only be cast for the duration of the turn that they were made? I thought they lingered indefinitely until cast.
Once you create a copy of a card with Garth, you can cast that copy only right after you create it, and not later. The effect "You may cast the copy" doesn't specify a duration (not even "this turn"), so you cast the copy this way while the ability is resolving, which is a moment that spells normally can't be cast, not even instant spells (C.R. 117.1a, 608.2g). See also this thread and this thread.
A copy of a card that is cast with Garth One-Eye is cast from outside the game (C.R. 707.13). Once cast, the copy is like any other copy of a card and like any other spell (C.R. 112.1b). For example:
If the spell cast this way resolves and is a permanent spell, it enters the battlefield (C.R. 608.3). (It will enter as a token if the game understands a "copy of a permanent spell" to include permanent spells that are copies of cards [C.R. 608.3b].)
If the spell cast this way resolves and is a nonpermanent spell, it goes to the graveyard and ceases to exist soon afterward (C.R. 608.2m, 117.3b, 117.5, 704.5e).
If the spell ends up in a zone other than the stack or the battlefield, it ceases to exist as a state-based action (C.R. 704.5e).
Thus, the copy of the card won't be in a player's hand or graveyard long enough for Timetwister or Thoughtseize to notice it, especially because for either spell, all players have to pass in a row for the spell to resolve but state-based actions have to be checked as players would get priority (C.R. 117.4, 117.3d, 117.5, 704.5e).
Thanks! So this means once the main game resumes, the copy of Shahrazad resolves and another subgame begins?
Shahrazad (or a copy of it) will already have started resolving (and will be on the stack) by the time it starts a subgame (C.R. 608.2, 608.2c). Once the subgame ends, the spell continues resolving and "each player who doesn't win the subgame loses half their life, rounded up". Note that Shahrazad (or a copy of it) can (directly) start only one subgame even if multiple spells named Shahrazad are on the stack.
For clarity, here is an illustration.
You cast Shahrazad and put it on the stack.
Retaining priority, you cast Twincast targeting Shahrazad.
All players pass, then Twincast resolves. Shahrazad is copied, then Twincast goes to the graveyard.
All players pass, then the copy of Shahrazad resolves. A subgame is played. Once the subgame ends, "each player who doesn't win the subgame loses half their life, rounded up". Then the copy of Shahrazad goes to the graveyard.
All players pass, then the original Shahrazad resolves. Another subgame is played. Once the subgame ends, "each player who doesn't win the subgame loses half their life, rounded up". Then the original Shahrazad goes to the graveyard.
Both Shahrazad and its copies (including the resolving Shahrazad spell) will stay on the main game's stack while the subgame is in progress (C.R. 608.2c; see also C.R. 722.1a). The subgame will have "an entirely new set of game zones" that, in general, have no connection to the main game's zones (C.R. 722.2).
For purposes of Cursed Totem and Crackdown Construct, loyalty abilities are activated abilities (C.R. 606.2). Thus, in particular, neither loyalty ability of Grand Master of Flowers can be activated while Grand Master of Flowers is a creature (before the ability started to be activated) and while Cursed Totem on the battlefield.
For purposes of devotion (C.R. 700.5) and mana value (C.R. 202.3), Old-Growth Troll's mana cost remains GGG. Old-Growth Troll's triggered ability changes only Old-Growth Troll's card types, subtypes, and abilities (C.R. 613.1d, 613.1f; see also C.R. 611.2e), and changes nothing else about Old-Growth Troll. (But compare Old-Growth Troll with Yedora, Grave Gardener, whose ability makes the returning permanent a "Forest land" but without a name or a mana cost, because the permanent enters the battlefield face down [C.R. 613.2b, 708.2a].)
For purposes of Aegar, a permanent was dealt "excess damage" if "one or more sources ... together dealt"—
as the case may be (C.R. 120.10). The trample ability, however, changes how combat damage is assigned, not how it's dealt (review C.R. 702.19).
- "At the beginning of each upkeep, if no spells were cast last turn, transform [this permanent]", and
- "At the beginning of each upkeep, if a player cast two or more spells last turn, transform [this permanent]".
The mechanics article, though, didn't state whether transforming double-faced cards with either ability will replace that ability with daybound or nightbound, respectively. Thus, it can be presumed that those cards won't change in this respect with the upcoming set.For example, players don't have priority to cast spells while an ability is resolving (C.R. 117.2e, 117.1a), so that my comment 2's second sentence applies accordingly to Sakashima's Student entering via ninjutsu or resolving as it does to Clone resolving. It likewise applies accordingly to Clone or Sakashima's Student entering the battlefield due to Aether Vial.
The triggered ability on Vesuvan Doppelganger targets a "creature" according to its Oracle text (C.R. 108.1, 115.1d). Thus, if that creature becomes illegal, the ability will fail to resolve (C.R. 608.2b).
In this sense, compare Curious Herd (and Dockside Extortionist and Alibou, Ancient Witness) with Archipelagore or Custodi Soulcaller, which both have abilities that contain an X that has to set in order for targets to be chosen (C.R. 603.3d, 601.2b; see also C.R. 107.3e). In contrast, Dockside Extortionist's ability doesn't require setting X as the ability goes on the stack (review C.R. 603.3c-d, 601.2). See also Necrologia, which requires you to choose an X in order to pay its additional cost (C.R. 601.2b, 601.2f, 108.1).
See also this submission on Reddit as well as this thread and this thread.
Thus, the copy of the card won't be in a player's hand or graveyard long enough for Timetwister or Thoughtseize to notice it, especially because for either spell, all players have to pass in a row for the spell to resolve but state-based actions have to be checked as players would get priority (C.R. 117.4, 117.3d, 117.5, 704.5e).
For clarity, here is an illustration.
EDIT: Clarification after comment 3 was posted.