Deadly Dispute was a common card printed in Adventures in the Forgotten Realms and Commander Masters: Battle for Baldur's Gate
When he attacks, you create a tapped/attacking token thats a copy of a Villain you control, but its also an Illusion that gets sacrificed on your next end step
Hitting for 6 and paying 2 mana to destroy two lands is a good way to annoy players, especially in EDH
Whether you mulligan slightly more or slightly less, so long as you're consistently falling in the "reasonable" part of the spectrum, you can feel like you're doing pretty well
There were four warriors-matter cards in Khans of Tarkir (all in WB) and four Gates-matter cards in Guilds of Ravnica (one blue, one Boros, and two artifacts, which makes sense considering its the play-all-the-colors archetype)
Not only does it give you graveyard value, but its a repeatable way to mitigate flooding