A 4-mana Orzhov Elder Dragon from Secrets of Strixhaven with flying vigilance that gives every instant and sorcery you cast casualty 1 — copy your removal by sacrificing a creature.
Sacrifice and Aristocrats decks. A steady token supply turns every instant and sorcery cast into a free copy, at the cost of a body the deck doesn't mind losing.
Removal-heavy control. Copying a board wipe or a piece of targeted removal for the price of a creature is one of the strongest applications of casualty available.
Flying tempo. Vigilance means it can attack and still hold up as a blocker, applying pressure while the casualty engine runs in the background.
How it does in Commander
As the commander
As the commander, Silverquill anchors a dedicated Orzhov sacrifice-and-spells deck — guaranteed access to casualty on every relevant spell from the command zone rewards building the 99 around both a token engine and a hand full of instants and sorceries worth copying.
In the 99
A strong support piece even outside a full build-around, since any Orzhov deck already running some sacrifice fodder gets real value from copying its best spells.
Formats it's strong in
Token-and-sacrifice decks. A cheap, renewable supply of bodies is exactly what casualty wants to be paid with, turning every relevant spell into a two-for-one.
Removal-heavy control shells. Copying board wipes and targeted removal is one of the single highest-value uses of casualty in the format.
Formats it's weak in
Decks with few creatures to spare. Without expendable bodies, the casualty cost means sacrificing something the deck actually needs, which is a real cost rather than a bonus.
Low instant/sorcery-count decks. The effect only matters as often as the deck is casting instants and sorceries in the first place.
Synergistic cards
Bitterblossom — A steady supply of expendable Faerie tokens that keeps the casualty cost free indefinitely.
Toxic Deluge — A board wipe that becomes devastating when copied for the price of a single creature via casualty.
Sign in Blood — A cheap draw spell that becomes doubled card advantage the moment it's copied off a token.
Any wide token generator — The more expendable bodies a deck can make, the more free spell copies casualty produces over a game.
Is it worth the price?
As a recent-set card, Silverquill, the Disputant is affordable and a reasonable pickup for an Orzhov sacrifice or control deck — low financial risk for a genuine spell-doubling engine.