
Artifact
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: Copy target triggered ability you control. You may choose new targets for the copy. (A triggered ability uses the words "when," "whenever," or "at.")

Also copies triggered abilities (plus activated/spells) for value.

Doubles ETB and other enter triggers, similar trigger-doubling role.

Doubles chosen-type creature triggers, another trigger multiplier.

Repeatable spell-copy engine artifact in similar value slot.

Copies activated abilities; pairs with similar combo-copy strategies.

Copies activated abilities of equipped creature for repeatable value.

Doubles your ETB triggers while shutting off opponents'.

Doubles wizard ETB triggers, another trigger-copy payoff.
→ Infinite blinking of nonland permanents, Infinite ETB, Infinite LTB
→ Infinite mana nonland permanents you control can produce, Infinite untap of nonland permanents you control
→ Infinite turns, Lock
→ Infinite copies of abilities you control on the stack, Infinite copies of a specific creature, Infinite creature tokens
→ Infinite +1/+1 counters on an infinite number of creature tokens, Infinite copies of abilities you control on the stack, Infinite creature tokens
→ Target opponent loses the game
Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]."
Strionic Resonator targets a triggered ability that has triggered and is on the stack and creates another instance of that ability on the stack. It doesn't cause any object to gain an ability.
The source of the copy is the same as the source of the original ability.
If the triggered ability is modal (that is, if it says, "Choose one —" or similar), the mode is copied and can't be changed.
If the triggered ability divides damage or distributes counters among a number of targets (for example, the ability of Bogardan Hellkite), the division and number of targets can't be changed. If you choose new targets, you must choose the same number of targets.
Any choices made when the triggered ability resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves. If the triggered ability asks you to pay a cost (such as that of Frenzied Goblin), you pay that cost for the copy.
If a triggered ability is linked to a second ability, copies of that triggered ability are also linked to that second ability. If the second ability refers to "the exiled card," it refers to all cards exiled by the triggered ability and the copy. For example, if Fiend Hunter's enters-the-battlefield ability is copied and two creatures are exiled, they both return when Fiend Hunter leaves the battlefield.
In some cases involving linked abilities, an ability requires information about "the exiled card." When this happens, the ability gets multiple answers. If these answers are being used to determine the value of a variable, the sum is used. For example, if Elite Arcanist's enters-the-battlefield ability is copied, two cards are exiled. The value of X in the activation cost of Elite Arcanist's other ability is the sum of the two cards' mana values. As the ability resolves, you create copies of both cards and can cast none, one, or both of the copies in any order.