While this isnt Lurrus of the Dream Den for a variety of reasons (it costs one more, cant be cast with black mana, isnt a companion), Lurrus taught us just how powerful being able to cast something from the graveyard every turn is
[74] The new system consisted of several interconnected circuits: The Player's Tour, The Magic Pro League, Challengers/Rivals, Tabletop Mythic Championships, and Arena Mythic Championships
It's never both, although it's an enchantment spell in either case
The mana values of these decks are quite low, meaning Dark Confidant shouldnt cost too much life
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Again, it's not card advantage in and of itself (since you draw three, and then discard three + lose the Coliseum), but it combines famously with Deep Analysis and madness cards (such as Circular Logic), and its effect can't be counterspelled