What happens when my opponent’s Akshan, Mischievous steals my equipped Shady Spectacles? What happens if they want to copy Aphelios?

If it was attached to a unit, the equipped unit loses its copy effect. Akshan will then become a copy of a friendly unit of his controller’s choice. If he becomes a copy of Aphelios, his ability will not trigger.

As of the Vendetta rules update, effects like Shady Spectacles and Svellsongur are replacement effects that replace the event of the equipment being attached to a unit with that event plus whatever their effect specifies.

In the case of Svellsongur, the resulting series of events will be: Attach → Copy the equipped unit’s text to Svellsongur’s effect text for as long as Svellsongur is attached.

For Shady Spectacles, the resulting series of events will be: Attach → Choose a friendly unit and make the equipped unit a copy of that unit for as long as Shady Spectacles is attached.

These events are not simultaneous. The attach event executes first, and then whatever event is instructed by the replacement effect is executed. Thus, the answer in the Spiritforged FAQ is no longer true: if you attach Svellsongur to Aphelios, he will not trigger twice. Svellsongur doesn’t have the copied effect text when the attach event executes.

Similarly, if Akshan nabs Shady Spectacles from an opponent, it will attach and then make him a copy. If his controller chooses to make him a copy of Aphelios, it’s too late by that point for his new triggered ability to see the attachment event; it’s already been completed.