Tricky Triggers, Trigger to watch out for in Gatecrash at Competitive REL

This set is full of triggers, including 4 of the new key-worded abilities. If you miss these triggers at competitive REL, you opponent can choose to have them not happen if they are beneficial.

Here is link to an explanation of the missed trigger policy

I'll start with the new keywords.

Evolve - if you miss your evolve trigger when your creature enters the battlefield you might not get the trigger if you have passed priority. Each instance of evolve triggers separately, and evolve checks power and toughness twice, once when the creature enters the battlefield and once when the evolve trigger resolves. It triggers when either the power of the creature entering is larger than the power of the creature with evolve, or the toughness of the creature entering is larger than than the toughness of the creature with evolve. If the creature with evolve has smaller power or toughness when a creature enters, but larger power and toughness when the trigger resolves, it will not get a counter. This can happen if multiple creatures enter at once. You can cast an instant or use an ability to boost the creature that entered power or toughness between when evolve triggers and when it resolves.*

If you cast a sorcery or creature, you have missed the trigger.

If you cast an instant, you COULD be casting it in response to the trigger, make sure you announce this if you are, or your opponent may call the judge.

If you change phase or end the turn, you have missed your trigger.

Evolve is not optional, and an opponent can decide if it happens or not.

*This interaction has confused some people, so I will give an example. If you had a 1/1 with evolve and two 2/2's entered the battlefield at the same time, evolve would trigger twice. Normally, when the first one resolves, your 1/1 becomes a 2/2. when the second resolves, your 1/1 is already a 2/2 so it would not get a counter as it no longer has lower power or toughness. What you could do is while the second evolve trigger is on the stack, Giant Growth the second 2/2. When the evolve trigger resolves, your 1/1 evolve is a 2/2, your 2/2 that just entered is a 5/5, so your 1/1 evolve would get a second counter, making it now a 3/3.

Extort- Extort is a MAY ability. It triggers every time you cast a spell. You may pay white or black once for each instance of extort on permanents you control each time you cast a spell.

If the spell resolves you miss the trigger.

I previously had written that if you pass priority, i.e. to see if an opponent counters, you had missed the trigger, but this is not currently the case. As long as the spell you cast is still on the stack, you have not missed the extort trigger.

Cipher- When a spell with Cipher resolves, you have to option to exile it and 'cipher' it on a creature. You must do this after the spell has resolved, after its other effects.

When you cipher a card, it goes from the stack to being exiled 'ciphered' on a creature, it never hits the graveyard. If you move the spell to the graveyard, you have opted to not exile it.

You choose the creature as it resolves, not when you cast the spell, and it does not target. Cipher happens as the spell resolves, so you cannot cipher if the spell was countered.

If you want to cipher a spell onto a keyrune, it must be a creature before the spell resolves. This means you must activate the keyrune before casting the spell, or maintain priority after casting the spell to activate it.

When a creature is encoded with a card it has 'Whenever this creature deals combat damage to a player, you may copy this card and you may cast the copy without paying its mana cost.' This means if another player gains control of a creature with cipher, that player also controls the cipher ability and may cast the cipher'ed spell.

Copying the ciphered card is optional, and you must chose to do it when you deal combat damage. If you move to the Main Phase, you have missed the cipher trigger.

Battalion - Battalion triggers in the declare attacker step, if you attack with a creature with battalion and at least 2 other creatures. This happens after attackers are declared, in the declare attackers phase.

The creatures do no have to be attacking the same person or planeswalker for battalion to trigger.

Battalion only checks the number of creatures attacking once, as it triggers. It does not matter how 
many creatures are attacking when the ability resolves.

Under the new IPG, Battalion triggers are missed when the game goes past the point where the trigger has a visible effect on the game. This means for a trigger that has a target (I.e. Firemane Avenger) when you change step you have missed the trigger. For triggers that would cause an opponent to make an illegal action (i.e. gives a creature flying) when you leave the declare blockers step. Up until then, you can announce the trigger and they have to block legally. For changes to combat (i.e. first strike) or power/toughness changes, you have until the combat damage step. If you leave the combat damage step you have missed the trigger.

As in any set, there are plenty of creatures with enter the battlefied effects. These are pretty easy to keep track of and hard to miss. They are all beneficial triggers except for Keymaster Rogue. If you miss them by casting another non-instant spell after the creature resolves, casting in instant but not in response to the trigger, or moving phases, you have missed the trigger. For all but Keymaster Rogue, it is up to your opponent for you to get the trigger or not. For Keymaster Rogue, the player will also get a warning.

All of the Guild Leaders have trigger associated with them. They are as follows:

(click their names for a link to their gatherer page)

Aurelia- Aurelia has a triggered ability that triggers when she attacks for the first time each turn.

It triggers when she is declared an attacker, and you must announce it before moving to declare attackers.

It untaps all creature you control, not just creatures you have declared as attacking. Creature are untapped in the declare attackers stage.

There is not an additional main phase, as many other effects that add combat phases add. If you move to your main phase after your first combat phase, you have elected to not use your second combat phase.

Lazav - Lazav's ability triggers whenever a creature card is put into an opponents graveyard from anywhere

It is an optional ability, and it trigger every time a creature card goes to the graveyard. If you pass priority after a creature card goes to the graveyard, you have missed the trigger.

If the creature card gets removed from the graveyard before Lazav's ability resolves, Lazav will still become a copy of that creature.

If multiple creature cards go to the graveyard at once, the ability triggers for each creature. Lazav's control controls the order in which they revolve. They can be responded to, meaning Lazav can become a copy of each one, and if they have an ability that can be used at instant speed, can use the ability in response to the next trigger.

The creature must go to the graveyard, if it is exiled, Lazav will not trigger. Tokens dying to not cause Lazav to trigger.

Borborymos - when Borborymos deals damage, his ability triggers. If you move from the combat step, you have missed the trigger and it is up to your opponent if you get it or not.

Obzedat - Obzedat has a may ability that triggers in your end step. If you pass the turn to your opponent you have elected to not use his ability so he will remain on the battlefield.

If you have elected to exile Obzedat, in your next turn Obzedat returns in your upkeep. If you do not return Obzedat, you have missed the trigger and it is up to your opponent if you get the trigger or not.

Gaining haste is part of the return trigger, you do no have to announce gaining haste on its own, as long as you have returned Obzedat in your upkeep.

Once Obzedat has gained haste, he has haste indefinitely. This is relevant if someone were to gain control of Obzedat in a way that does not also grant him haste.

If you have gained control of Obzedat, it returns under it OWNERS control if you elect to exile him.

Prime Speaker Zegana - Prime speaker enters with counters already on here, this is not a trigger ability. It happens as it resolves and enters the battlefield, if you want to boost a creatures power and toughness, you either have to do it before casting Prime Speaker, or maintain Priority and do it after.

When it enters, it has a triggered ability to draw cards equal to its power. The number of cards drawn is determined by the power as this ability resolves. This can be responded to by boosting her power to draw more cards.

If you cast another non-instant spell or change phases, you have missed the trigger.

There are many other triggers, most associated with creatures, but some are on enchantments or artifacts too.

Duskmantle Guildmage - If you active his first ability, it is up to you to keep track of whenever a card goes into your opponents graveyard. If you move on, you have missed the trigger. It triggers separately for each card that enters you opponents graveyard, and for each time you have activated the ability. (If you opponent is playing to fast, you will probably still be able to make them lose life within the same phase, but don't take the risk)

Vizkopa Guildmage - Similarly to Duskmantle Guildmage, you control the trigger for the second ability and must announce it whenever you gain life. If you move on after gaining life, you have missed the trigger.

Master Biomancer - Creatures enter with counters equal to Master Biomancer's power, it is not a trigger ability. If you wish to boost Master Biomancer's power, you must do it before you cast another creature, or after but while maintaining priority.

Experiment One - Be damage is already marked on Experiment One and you decide to remove counters to regenerate him e.g. he is a 1/1 with two +1/+1 counters making him a 3/3, you block a 1/1 in combat, an opponent casts mugging post combat targeting Experiment One. If you remove two counters to regenerate him, he will die due to becoming a 1/1 with 1 damage marked on him from combat, before he can regenerate.

Boros Reckoner, High Priest of Penance - These abilities triggers whenever it is dealt damage by any source, including a source you control. If you pass priority after it is dealt damage, you missed the trigger.

Guardian of the Gateless - When you declare it as a blocker, you must announce the trigger. If you move to the combat damage step you have missed the trigger, and the guardian may die in combat.

Whenever ~ deals combat damage - this is on a number of creatures. If you have dealt combat damage with that creature, and leave the combat phase, you have missed the trigger. This is a detrimental trigger on Leyline Phantom and will result in a warning. For all others, it is up to your opponent if it happens.

At the beggining of your upkeep... - This triggers in your upkeep and is on multiple cards, both creature and enchantments. You must announce the trigger and make your opponent reveal a card. If you move to your draw step, you have missed the trigger and it is up to your opponent if it happens

Whenever ~ attacks/blocks - This triggers in the declare attackers/declare blockers step. You must announce the triggers when you declare a creature as an attacker or blocker. If you move step to the blockers or combat damage step respectively, you have missed your trigger.

And as bearrosaurus added, don't let anyone Bloodrush a creature enchanted with a Holy Mantle.

This only applies at Competitive REL under the new missed triggers rule. This is meant as a guide to ensure you do not miss any of your own triggers and get a judge called on you. If you opponent misses their triggers, you have every right to call a judge yourself and not let them get their beneficial triggers too.

With the new IPG released today, there have been a few minor changes. The only thing that has changed in the guide is when a trigger is officially missed. It has now changed to when the trigger would have effected the game state instead of when it resolves. This means Battalion is now missed at different times for different triggers. If the trigger first effects the combat damage step (power/toughness boost, first strike, indestructabe) the trigger is only missed after the combat damage step. If the trigger is direct damage (Firemine Avenger, Bomber Corps) The trigger is missed when you change step to declare blockers. If the trigger causes illegal blocks (giving creature flying) it is missed if you go past the declare blockers step.