Leyline of the Void exiles anything that would go to an opponent's graveyard, so it shuts off the self-mill from Malevolent Rumble and keeps their graveyard empty, which holds down Emrakul's cost reduction (it scales with card types in their graveyard) and Shifting Woodland's delirium. It only affects opponents' graveyards, so our own Unearth, Psychic Frog and Abhorrent Oculus still work off our graveyard as normal. Harbinger of the Seas turns Eldrazi Temple, Urza's Saga, and Ugin's Labyrinth into plain Islands, crippling their colorless ramp. Spell Pierce and Force of Negation can only hit noncreature spells, and their key threats (Emrakul, Devourer of Destiny, Sowing Mycospawn, Basking Broodscale) are all creature spells, so these two are weak here. Keep Fatal Push and Counterspell in to answer Basking Broodscale and Emrakul respectively.