2 pieces — Creeping Spores: Damaging ability hits build Spore Charges, at most once every 0.5 seconds. At 3 charges, your next damaging ability plants a mushroom that erupts for 15% of that hit.
4 pieces — Violent Bloom: The mushroom erupts for 30% of the triggering hit in a 90-unit area, damaging up to 5 enemies.