Those intervening if clauses

Some triggered abilities read “Trigger event, If condition, Effect.”
These are known as intervening if clauses, and their condition is checked twice – once when the ability is put on the stack, and once when it resolves.
If the condition isn’t met right from the start, the ability won’t trigger. If it does trigger, but the condition isn’t met when the ability tries to resolve, the ability is removed from the stack and does nothing. Otherwise, it continues to resolve.

* Faerie Miscreant’s triggered ability checks to see if you control another creature named Faerie Miscreant at the time the new Faerie Miscreant enters the battlefield. If you don’t, the ability won’t trigger at all. The ability will check again as it tries to resolve. If, at that time, you don’t control another creature named Faerie Miscreant, the ability will have no effect.

However, it is important to note not everything that seems like an intervening if clause is actually one:

* If Erebos’s Emissary is an Aura and is destroyed in response to its activated ability, the enchanted creature will still get the bonus.

In this case it’s actually an activated ability, not a triggered one.
Another example

* Whether you control a creature with a +1/+1 counter on it is checked only when the ability resolves. Notably, if Chronicler of Heroes entering the battlefield causes an evolve ability to trigger, you can have the evolve ability resolve first and then draw a card.

In this case the triggered ability doesn’t follow the “Trigger event, If condition, Effect” structure, so it’s not an intervening ‘if’ clause. More specifically, “When Chronicler of Heroes enters the battlefield, draw a card” isn’t an event because of the last part.

Each player
If an effect says each player does something, first the active player (the player whose turn it is) will choose what to do, then each other player in turn order will do the same. Then all those choices will happen at the same time.

* When a spell or ability instructs each player to discard a card, starting with the player whose turn it is and proceeding in turn order, each player selects a card from his or her hand without revealing it, sets it aside, and then all of those cards are revealed and discarded at once.

Good things come in pairs (or more)
Whenever a group of permanents enters or leaves the battlefield together, the game looks back in time just a bit, to see what entered or left. Permanents will see other permanents that arrived or left at the same time with them, and will trigger accordingly.

* If Pious Evangel enters the battlefield at the same time as another creature you control, Pious Evangel’s ability triggers once for the other creature as well as once for itself.

* If Wayward Disciple dies at the same time as another creature you control, Wayward Disciple’s ability triggers once for the other creature as well as once for itself.

This “looks back in time” can sometimes cause not so obvious situations:

* If Diregraf Colossus enters the battlefield from your graveyard, its first ability will count itself among the Zombie cards in your graveyard. Similarly, if it enters the battlefield at the same time as another Zombie card enters the battlefield from your graveyard, the ability will count that other Zombie.

* Diregraf Colossus’s last ability won’t trigger when you cast it because it’s not on the battlefield yet.

Duration of a spell or ability
When a spell, activated ability, or triggered ability resolves, it may create one or more one-shot effect, or continuous effects.
A one-shot effect does something just once and doesn’t have a duration. These include dealing damage, destroying a permanent, creating a token, and moving an object from one zone to another.
A continuous effect generated by the resolution of a spell or ability lasts as long as stated by the spell or ability creating it (such as “until end of turn”). If no duration is stated, it lasts until the end of the game.

* The control-changing effect lasts indefinitely, even if the power of the creature becomes greater than the number of creatures you control after the ability resolves.

Some continuous effects apply to game objects, modifying the characteristics or changing the controller of any objects. In that case the set of objects it affects is determined when that continuous effect begins. After that point, the set won’t change.
Effects that say “until end of turn” are usually of that kind.

* The set of creatures affected by Hazardous Conditions is determined as the spell resolves. Creatures that get a counter later in the turn will continue to get -2/-2. Creatures that enter the battlefield or lose their counters later in the turn and noncreature permanents that become creatures later in the turn won’t get -2/-2.

Other continuous effects modify the very rules of the game, so they can affect objects that weren’t affected when that continuous effect began.
Effects that say “this turn” are usually of that kind.

* Because Magmatic Chasm’s effect doesn’t change the characteristics of any permanents, the set of creatures affected by Magmatic Chasm is constantly updated. Creatures without flying that enter the battlefield later in the turn won’t be able to block.

Here’s another neat example, mixing up the two

* Only creatures on the battlefield when Death Frenzy resolves will get -2/-2. However, if a creature enters the battlefield and then dies later that turn, you’ll gain 1 life for it.

Cherries on top
If a creature has * as its power or toughness, the ability defining it works in all zones, not just the battlefield.

If something lets you tap a creature for an effect, but doesn’t use the {T} symbol, you may tap creatures that haven’t been under your control continuously since the beginning of your most recent turn.

Here’s an example that incorporates the two:

* The ability that defines Veteran Warleader’s power and toughness works in all zones, not just the battlefield. If Veteran Warleader is on the battlefield, it will count itself.

* To activate the last ability, you can tap any other untapped Ally you control, including one that hasn’t been under your control since the beginning of your most recent turn. (Note that ability doesn’t use the tap symbol.)

* You choose which ability Veteran Warleader gains as the last ability resolves, not as you activate it.

Noncreature permanents that become creatures are subject to summoning sickness, unless they have haste. This is checked against when that permanent itself came under your control, not when it became a creature, or when it entered the battlefield under someone else’s control.

* A land that becomes a creature may be affected by “summoning sickness.” You can’t attack with it or use any of its {T} abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature nor when it entered the battlefield.

And a little extra something for the end…
An “extra turn” is any turn created by a spell or ability. Notably, it doesn’t include additional turns taken in tournaments after time expires for a round.

That’s all folks!
Soon the Aether Revolt release notes will be published (If they haven’t already) and hopefully you’ll be able to see how everything you’ve read here ties up.

Thanks to Callum Milne, David de la Iglesia, George Gavrilita, Georgi Benev & Nathan Long for all their help with these articles.
Thank you for reading.