Let me see if I can get all of this right...

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PART 1: Played abilities

1. Active player declares that they are playing an ability, pays costs and selects targets.
--> This ability has been "used". Choke happens here.

2. Resolve the effect
--> Nothing can interrupt effect resolution, so anything that might be triggered would come after effect resolution***.

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PART 2: Passive abilities

1. The game reaches a point where some passive ability would be applicable
--> The controller of that ability has now "used" it, even if they have no intention of taking advantage of any options it might provide.
--> Choke happens here, before the game continues on to whatever situation the passive ability applies to.

i.e. You "use" Unit Guard as soon as the game reaches that step, before and regardless of whether you choose to make that particular guarding decision.

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PART 3: Triggered abilities and reaction spells

Whenever an event that could cause a triggered ability or reaction spell occurs:

1. Each player (active player first) must declare intent to play a reaction spell if they wish to do so. They must name the spell they wish to use*. Additionally, intention must be declared for any optional (has text like "you may pay cost to do x") triggered ability.

2. Handle all declared spells/abilities, and any mandatory triggered abilities, in an order that the AP determines**. For each, its controller:

a) Pays the cost (if any) and selects targets
--> The ability has now been "used", so Choke happens here

b) Resolves the effect
--> Nothing can interrupt effect resolution, so anything that might be triggered would come after effect resolution but before the next spell/ability in the queue is used


* In the course of natural gameplay, the inactive player may be the first one to mention that they have a reaction spell, but they don't technically have to name it until the active player has declared and named all of their reactions/triggers

** The AP does not need to lay out the full sequence up front; they can pick one ability, it gets fully resolved, then they pick the next, and so on. However, all declared abilities and spells must ultimately be played if possible.

If the AP chooses to handle an opponent's ability at a point when it has no legal targets, then that ability simply does not get used?

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***BONUS: "Speed" of various things

As it relates to what sorts of things can interrupt what, what things have to wait etc. I think it's like:

1. Players winning/losing the game

2. Completion of an effect's resolution

3a. The -initiation- of a destruction sequence
3b. The -initiation- of a damage resolution sequence

4. Triggered abilities and reaction spells

5. The procession of a damage / destruction sequence

6. Anchornaut, and other open-ended "during your turn" things

7. The procession of a combat sequence

8. The playing of main and side actions

Or are 1 and 2 flipped? 6 and 7 could be flipped as well; it'd make more sense that way, but I feel like I've read otherwise.

But the meat of this question is 3 through 5 - as I understand it, once an effect has resolved, any damage or destruction that occurred during it has to be handled before anything triggering off of other parts of the effect can even be declared.

However, triggers and reactions spells and such are allowed to interrupt the resolution of a damage or destruction sequence (obviously, else Sympathy Pain and Final Cry wouldn't work).

So i.e. my opponent activates Summon Gilder, targeting my Anchornaut. Ice Trap is not even a twinkle in my eye, because the effect resolution cannot be broken nor the ensuing entry into a damage resolution sequence.

I cannot use Anchornaut before the damage resolves to a wound, or before its destruction sends it to my discard pile. I can, however, Sympathy Pain the Gilder before Anchornaut gets a wound, which would send us into a new ("stacked") damage sequence. I can also trigger my two Chant of Revenges upon the Anchornaut's destruction (before it goes to discard).

But Ice Trap would need to wait (if I haven't played some other Reaction Spell) until Anchornaut is in the discard pile and we have no other pending reactions to that (i.e. Screams). Only then do players go about declaring any reactions or triggers to the Gilder entering play.

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Am I close to getting all this down?