Re-Stacked and Re-Pact

Arthur and Neil are playing in a Modern PPTQ. At the end of Arthur’s turn, Neil taps out to cast Peer Through Depths. Arthur responds with Dispel. Neil responds with Pact of Negation. Arthur thinks for a moment, then casts Spell Pierce.

Neil pauses, says “Ah, nuts…” then puts his spells in his graveyard. Arthur does the same.

Neil untaps and draws for his turn.

Arthur says, “You didn’t pay for Pact.”
Neil replies, “You Spell Pierced it.”
“No, I Pierced the Peer Through Depths.”

What do you do?

Since Arthur didn’t state he was targeting Peer Through Depths with Spell pierce, he is assumed to be targeting Pact of Negation as per MTR 4.2. Nothing happened that would result in a warning or back-up, educate the players about the Tournament Shortcut and the need to be clear in communicating intended game actions, and have the players continue.

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