the triggered ability triggers when (at the exact moment that) Zegana enters the field
the trigger goes on the stack moments later (but not exactly the same time) eg. let's say you put Zegana on the field with Unburial Rites , she's put on the field as Rites is resolving, but the trigger doesn't enter the stack until after Rites fully finishes resolving, though her trigger did trigger while Rites was resolving
the trigger resolves and the cards are drawn a bit after that (after someone has time to respond with Murder and there's even time for Murder to resolve)
MtG Rules Advisor & Goth/Industrial/EBM/Indie/Alternative/80's-Wave DJ DJ Vortex
DCI Certified Rules Advisor from July 14, 2009 to July 14, 2012 DCI #5209514320
Wit found in Rules Q&A
RPJesus: "Man, screw the rules, I'll play a game of 2HG Archenemy Planechase Emperor EDH draft yet. Once I figure out the rules for it..." Chaikov: "Of course, casual Magic may be played any way your Pokemon group agrees on..." and "It's not logic. It's Magic!" GainsBanding: "I only play online. The Magic Online shuffler is AWESOME!" Ikegami: "one might think [adult cats] would make excellent tokens. The issue, though, is that they are very hard to exile. They return to the battlefield more often than an undying creature." Astarael7: "Does 121.1 imply that players are supposed to wear their poison counters?" Bimmerbot: "If you move the wrong way and [the poison counters] fall, it's a game rule violation" Helluminatus: "Just remember, if it looks like a duck, smells like a duck, and quacks like a duck, but the oracle text says creature - Bunny , then by god, it's a bunny." MadCow21: "Who are you and what have you done with the real Chaikov?"
Ok. So, in the case you describe, there would be (at least) two chances to respond, right? You could counter Unburial Rites with something, or choose to let it resolve and then after Zegana resolves (and therefore her triggered ability resolves), play something in response.
If you chose to let Zegana enter the field, you could then Murder her. In this case, her last known power was 4 and the player who put her on the field will get to draw 4 cards.
If you chose to let Zegana enter the field, you respond with as Enigma256 suggested with Dismember , Zegana gets -5/-5 giving her a resultant P/T of -1/-1. In this case her last known power was -1, so the player who put her on thefield will get to draw 0 cards.
choose to let it resolve and then after Zegana resolves (and therefore her triggered ability resolves)
STOP RIGHT THERE!
these are two distinct events - the trigger triggering and the trigger resolving (actually there's a third distinct event between the two of them: the trigger entering the stack)
Zegana enters the field and her ability triggers..... but it doesn't do anything yet
at the first available opportunity, the trigger goes on the stack (just like a spell would when you cast it) in this case, after Rites finishes resolving
now players can respond to the trigger on the stack (like they can respond to a spell) say with a Voidslime to counter the trigger
after all players pass with that trigger as the top object on the stack, it finally resolves and then finally cards are drawn as it's resolving
also note: Zegana doesn't resolve when put on the field by Rites, only spells and abilities resolve she wasn't cast as a spell (she's merely put on the field from the yard) and she's not an ability
MtG Rules Advisor & Goth/Industrial/EBM/Indie/Alternative/80's-Wave DJ DJ Vortex
DCI Certified Rules Advisor from July 14, 2009 to July 14, 2012 DCI #5209514320
Wit found in Rules Q&A
RPJesus: "Man, screw the rules, I'll play a game of 2HG Archenemy Planechase Emperor EDH draft yet. Once I figure out the rules for it..." Chaikov: "Of course, casual Magic may be played any way your Pokemon group agrees on..." and "It's not logic. It's Magic!" GainsBanding: "I only play online. The Magic Online shuffler is AWESOME!" Ikegami: "one might think [adult cats] would make excellent tokens. The issue, though, is that they are very hard to exile. They return to the battlefield more often than an undying creature." Astarael7: "Does 121.1 imply that players are supposed to wear their poison counters?" Bimmerbot: "If you move the wrong way and [the poison counters] fall, it's a game rule violation" Helluminatus: "Just remember, if it looks like a duck, smells like a duck, and quacks like a duck, but the oracle text says creature - Bunny , then by god, it's a bunny." MadCow21: "Who are you and what have you done with the real Chaikov?"
Hm, one bit I am missing, is why you can't murder her, but you can dismember her.
Namely, they both target the enemy creature as it enters the field.
So, the spell resolves, and enters the battlefield, card drawing trigger goes on the stack. Now, you can cast both murder and dismember on her, while the ability is on the stack, and they will resolve before the CDT resolves. In both cases, she dies while the trigger is still on the stack, so I am assuming that just because the creature dies, doesnt mean its triggered ability is kept from resolving.
In the murder case ( ) , when a creature dies, it loses the counters on it, so would be reduced back to a 1/1 and thus when the trigger checks for the power of the card in order to resolve, it should only draw you 1 card as the counters are knocked off by the murder. In the dismemberment case, just about the same thing happens; her power and toughness is reduced and she dies, then the abilty resolves. However, whle her P/T on the board would be -1/-1, she is dead by the point we need to resolve the trigger, and it is my impression that once a card goes into the graveyard, it is no longer a -1/-1, but would instead revert to the basic 1/1 on the card, as the card is already dead by the time it is time to check against the p/t for the CDT.
You can do either one. If you murder Zegana, the Last Known Information is whatever the power and toughness was as the spell resolved. While Murder oves her to the graveyard and she does lose those counters, she probably -had- counters while she was on the battlefield and that's the information the game will use.
If you Dismember Zegana and she drops to 0 toughness or less, she will be put into the graveyard as a state-based action. When the game looks at Last Known Info to see what she looked like at her last point on the field, it will see 0 or less toughness and let you draw that many cards when the ability resolves (basically, you won't draw any)
It's the same way a Mogg Fanatic equipped with a Basilisk Collar deals lifelink and deathtouch damage even if it's sacrificed and in the graveyard. When the ability resolves, the game looks back for LKI and sees what it looked like on the battlefield.
Hm, one bit I am missing, is why you can't murder her, but you can dismember her.
Namely, they both target the enemy creature as it enters the field.
Murder and Dismember both target a creature, which means a permanent on the battlefield with the Creature type. You can cast either at Zegana after she resolves.
By this time (a) she has gained counters from her own static ability (unless she's the only creature you control, of course) and her triggered ability has fired and been put on the stack.
So, the spell resolves, and enters the battlefield, card drawing trigger goes on the stack. Now, you can cast both murder and dismember on her, while the ability is on the stack, and they will resolve before the CDT resolves. In both cases, she dies while the trigger is still on the stack, so I am assuming that just because the creature dies, doesnt mean its triggered ability is kept from resolving.
That is correct, yes. An ability on the stack is completely independent of its source, unless something makes it check the source.
In the murder case ( ) , when a creature dies, it loses the counters on it, so would be reduced back to a 1/1 and thus when the trigger checks for the power of the card in order to resolve, it should only draw you 1 card as the counters are knocked off by the murder.
This is where you are going wrong.
Murder causes the creature to leave the battlefield. Since the creature is now dead, we check the gamestate the creature last existed in and determine its power. At that point the creature's power was still affected by the counters. Therefore you draw a number of cards equal to that power.
In the dismemberment case, just about the same thing happens; her power and toughness is reduced and she dies, then the abilty resolves. However, whle her P/T on the board would be -1/-1, she is dead by the point we need to resolve the trigger, and it is my impression that once a card goes into the graveyard, it is no longer a -1/-1, but would instead revert to the basic 1/1 on the card, as the card is already dead by the time it is time to check against the p/t for the CDT.
Again, since Zegana is dead, you check the last gamestate in which she was still on the battlefield. This is the gamestate after Dismember has fully resolved, but before the subsequent SBA check that will cause her to drop dead of negative toughness. At that point her power will be less than zero, so you draw that many cards - ie none.
Also, quite interesting how simic causes a LOT of rules questions before even being released.
Hm. Another thing to make sure I got this right;
You cast her,ability goes on the stack, she gets dismembered, I respond with a Simic charm ("Choose one - Target creature gets +3/+3 until end of turn; permanents you control gain hexproof until end of turn; or return target creature to its owner's hand.") to toss her back onto my own hand, she still gives full amount of cards, since that was her last state, correct?
But, this also means that I can put the trigger on the stack, and pump her with +3+3 to draw 3 extra cards before she resolved, right?
And, in the case of the bouncing her back in response to the enemy spell, since she still needs to enter the battlefield for any of this to happen, she will trigger evolution in spite of the bounce, and the evolution triggers on other creatures should happen in spite of the dismember, since the evolution trigger checks for power when she enters, aka before the dismember can be cast on her, and thus her power going lower shouldnt affect evolve since that was already checked for before, correct?
E.g, I cast her, she enters as a 5/5 ( i have a biomancer in play, so 2 counters + 2 from his power and her own 1 power), they cast dismember. But since she was 5/5 when she entered, I put the evolve trigger for my 2/4 on the stack right away, even if she later turns into a 0/0, and since her entering the battlefield is when you check for the trigger, and not when the evolve resolves, her going 0/0 later should not affect that trigger at all, right?
You cast her,ability goes on the stack, she gets dismembered, I respond with a Simic charm ("Choose one - Target creature gets +3/+3 until end of turn; permanents you control gain hexproof until end of turn; or return target creature to its owner's hand.") to toss her back onto my own hand, she still gives full amount of cards, since that was her last state, correct?
And, in the case of the bouncing her back in response to the enemy spell, since she still needs to enter the battlefield for any of this to happen, she will trigger evolution in spite of the bounce, and the evolution triggers on other creatures should happen in spite of the dismember, since the evolution trigger checks for power when she enters, aka before the dismember can be cast on her, and thus her power going lower shouldnt affect evolve since that was already checked for before, correct?
we need to wait for the complete rules of Evolve for that, but I suspect that the power is rechecked on resolution, so if it is no longer higher than the evolving creature it will do nothing
The draw trigger checks her power when it resolves, if she's not on the field at that time, it looks at what her power was at the the last moment she was on the field.
If someone casts Dismember at her and it resolves and her toughness drops to 0 or less, she'll die before anyone can do anything, however, players can respond to Dismember being cast with Simic Charm, so yes, you could bounce her to your hand and her power would be frozen at that moment in time for her trigger, you could give her +3/+3 which might save her from the Dismember, but would likely cause you to draw fewer cards for her trigger or you could give her hexproof and Dismember would be countered.
MtG Rules Advisor & Goth/Industrial/EBM/Indie/Alternative/80's-Wave DJ DJ Vortex
DCI Certified Rules Advisor from July 14, 2009 to July 14, 2012 DCI #5209514320
Wit found in Rules Q&A
RPJesus: "Man, screw the rules, I'll play a game of 2HG Archenemy Planechase Emperor EDH draft yet. Once I figure out the rules for it..." Chaikov: "Of course, casual Magic may be played any way your Pokemon group agrees on..." and "It's not logic. It's Magic!" GainsBanding: "I only play online. The Magic Online shuffler is AWESOME!" Ikegami: "one might think [adult cats] would make excellent tokens. The issue, though, is that they are very hard to exile. They return to the battlefield more often than an undying creature." Astarael7: "Does 121.1 imply that players are supposed to wear their poison counters?" Bimmerbot: "If you move the wrong way and [the poison counters] fall, it's a game rule violation" Helluminatus: "Just remember, if it looks like a duck, smells like a duck, and quacks like a duck, but the oracle text says creature - Bunny , then by god, it's a bunny." MadCow21: "Who are you and what have you done with the real Chaikov?"
) , when a creature dies, it loses the counters on it, so would be reduced back to a 1/1 and thus when the trigger checks for the power of the card in order to resolve, it should only draw you 1 card as the counters are knocked off by the murder. 
