Grixis Reanimator aims to cheat large threats into play early via the graveyard, so Soul-Guide Lantern is your highest-priority sideboard card — it provides cheap graveyard hate that disrupts their core plan without slowing your landfall engine. Mossborn Hydra comes in as a resilient, scalable threat that can match or outclass their reanimation targets in the late game. Meltstrider's Resolve and Royal Treatment are low-impact against a deck that typically ignores auras and isn't trying to interact with individual creatures early, while Escape Tunnel's land-cycling role is less critical here than having answers to their graveyard. Keep your core landfall package intact since the ability to go wide and tall quickly puts pressure on their combo and forces them to find answers rather than setting up reanimation.