"Akal theorizes that it is some sort of signal, resonating beyond this cavern's physical space. But if so, who—or what—is the signal for?"
—Huatli's travel journal

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

Strionic Resonator

The Lost Caverns of Ixalan Commander

Its tines cannot be rung by mere physical force. Only magic of great power can start its eldritch resonance.

March of the Machine Commander

Nobody knew what the relic did, only that it was growing louder.