Rare crafting materials like Rotting Fungi, Mycelium Resin, Vile Blood, and Cursed Sulfur.
Unique loot such as fungus-infused gear and POE2 Currency toxic-enhanced equipment.
Crafting recipes that can only be obtained through these boss events.
Mycelium Fragments used to unlock additional Vile Alchemist services and potions.
Event and Boss Mechanics
When these bosses spawn, they will typically follow these patterns:

Spawn Locations: Bosses will spawn in areas marked by toxic pools, spore clouds, or fungal-covered caves.
Special Attacks: Fungal bosses often have poisonous area attacks, spore missile barrages, and decay-based effects that apply debuffs to players.
Environmental Hazards: The environment itself may be hazardous during these events, with poison clouds or fungal spores that need to be avoided to stay alive.
Group Play for Enhanced Events
Cooperative Multiplayer: Some of the more challenging fungal boss events require a team. Coordinate with other players in the Grim Tangle region, as these events may involve difficult environmental hazards and multiple stages.
Bonus Rewards: Group events can provide additional fungal crafting resources and higher-tier loot drops, rewarding players with fungus-infused potions and rare fungal crafting materials.
Conclusion
Unlocking fungal boss events is an exciting part of progressing through the Grim Tangle zone in Path of Exile 2. Keep an eye out for quest completions, mini-boss kills, and special events to trigger these fights. By defeating these bosses, you’ll gain access to valuable materials for potions, gear crafting, and unlock more opportunities in the Vile Alchemist's Workshop and Sporemerchant crafting systems. Be prepared for a tough battle as you fight to buy POE 2 Currency rid the land of the fungal corruption!