The short answer: the referee decides
Arcbound Tracker Aria of Flame Artifact Blast Blazing Bomb Burnout Caldera Pyremaw Captain Ripley Vance Chandra, Acolyte of Flame Cinder Strike Cunning Bandit Death-Greeter's Champion Dwarven Forge-Chanter Flametongue Yearling Flaming Tyrannosaurus Geistflame Reservoir Goblin Artisans Heartfire Hero Imminent Doom Kami of Celebration Mages' Contest Memory Worm Mica, Reader of Ruins Molten Influence Origin of Thor Overlord of the Boilerbilges Pyroblast Red Elemental Blast Reduce // Rubble Runescale Stormbrood Spectacular Showdown The Great Work Tibalt's Trickery
Price depends on the character, the set, the print run, condition, and current demand
In a Control deck like this, which plans to go long and grind things out, Emet-Selchs back half is also very relevant
This powerful Vehicle can easily morph a board stall into a tattered wasteland on your opponent's side
Plenty of commentators had opinions to share after the event, and an image of the incident went viral, becoming an instant meme