Grixis Reanimator wants to discard Archon of Cruelty or Abhorrent Oculus and bring it back cheaply with Persist or Unearth, so you need to attack the graveyard plan directly. Consign to Memory exiles Unearth or Persist on the stack, or removes a reanimated Archon of Cruelty before its enter-the-battlefield trigger resolves, making it the single best card in the matchup. Harbinger of the Seas provides a proactive clock and a solid blocker while grinding through a mirror-ish matchup where board presence matters. Spell Snare is mostly narrow here and Sink into Stupor only buys a turn against a deck that can just reanimate again, so both are cut for graveyard hate.