Aphelios, Exalted

Aphelios triggers once when either Svellsongur or Shady Spectacles is attached to him. A different unit that becomes a copy of Aphelios through Shady Spectacles does not trigger.

Both equipment abilities are replacement effects because they describe an action that happens "as" the equipment is attached.^[369.1] Each replaces the single attachment event with that same attachment event plus its copy action.^[370.1.b.1] This does not create a second attachment event: events are simultaneous only when they result from the same game action,^[370.1.a.2] and copying is a separate game action added to the attachment event by the replacement effect.

Aphelios's trigger condition is evaluated after the attachment event is processed.^[383.2.c] At that point, he still has his printed ability, so the game adds one pending trigger to the chain before continuing the equipment's replacement effect and performing its copy action.^{[401.1][401.2]}

With Svellsongur, that pending trigger is created before Svellsongur copies Aphelios's effect text. The newly copied text does not look back and trigger from the attachment that already occurred, so there is no second trigger.

With Shady Spectacles attached to Aphelios, his trigger is similarly created before he becomes a copy of the chosen unit. If Shady Spectacles is instead attached to another unit and that unit becomes a copy of Aphelios, the unit did not have Aphelios's ability when the attachment event occurred, so it does not trigger at all. Treating either copy action as another attachment and triggering Aphelios twice is therefore not consistent with the current rules.