Hero card

Agatha's Soul Cauldron

Legendary Artifact

SpellUsed once: what it does depends on when you cast it

Needs: Valiant

Gives: Counter +1/+1, Artifacts, Legendary

Not in winning lists yet: read from the card text and the graph

Build a deck with Agatha's Soul Cauldron as the hero

Makes it work

Seedglaive Mentor

Benefits from it

Costume Closet · Tidus, Blitzball Star · Elvish Archivist · Donatello, Way with Machines · Captain Storm, Cosmium Raider · Mm'menon, Uthros Exile · Aatchik, Emerald Radian · Dockworker Drone

Use instead if you don't have it

Collector's Cage · Costume Closet · Explorer's Cache · Astrologian's Planisphere · Lost Jitte · The Ooze

Cards in the meta that answer it

Countersculpt (Azorius Control) · Inevitable Defeat (4-Color Control) · No More Lies (Azorius Control) · We Say Thee Nay! (Dimir Aggro)