Living End cascades into its namesake Sorcery to reanimate a full graveyard of cyclers like Street Wraith and Generous Ent, so both Tormod's Crypt and Surgical Extraction are excellent proactive answers that can strip their graveyard before the cascade even happens. Surgical Extraction on a cycled card can remove their entire Living End package from the graveyard, effectively countering the spell before it's cast. Two copies of Mishra's Bauble and one Mutagenic Growth come out since they don't interact with the combo and you need graveyard hate online as early as possible. Watch for Force of Negation and Subtlety protecting their combo, so try to strip the graveyard before they have mana up to protect it, ideally on your own turn.