This is the only boss in Sporefall and is a single phase fight involving a lot of add management.
Normal/Heroic:
Start tanking the boss where it stands. Raid start behind boss.
Boss pulses constant and increasing raid wide damage - this eventually is the "soft enrage".
Putrid Fist: tank swap.
Awakening Fungi cast - multiple green circles with flowers, plus one blue with a mushroom. Pull boss to the blue circle.
Normal: Small Shroomling fixating adds spawn from green circles .. avoid circles and stack on boss to AoE down.
Heroic: Additional Sporecap add spawns at blue circle - they will not move - interrupt & kill. For first set of Shroomlings, just drag boss to this and cleave down.
For second set, ranged dps switch to this and nuke.
Mythic: Additional Fungling adds spawn from green circles fixate on players. (Their corpses can never be within 10 yds of Shroomling corpses). Kite near to Sporecap add and kill each type of add in their own tight pack, without getting too close. Shroomlings at front of boss, Funglings at the back of the boss.
Festering Vines: Green circle around players with reduced movement speed. Move to outside edge to drop.
Fungal Bloom: every add body becomes a bursting mushroom .. kill before they finish their casts. Split raid to do this.
Mythic: Usually at least one bursting mushroom will finish its cast - stack up for healer CD's.