Alchemical Hydra
The fight is instanced; if players die while fighting the Hydra, then they may reclaim their items from Orrvor quo Maten outside for 100,000 coins each time. Dying elsewhere with items still held by him will result in them being lost forever.
While the Hydra is in the room, players cannot leave through the doors, as they are jammed when this occurs. Teleports will still work, however. The Hydra has a respawn time of 20 seconds.
The Hydra has four phases, each one beginning upon each 25% health threshold (~275 health). A head will fall off each time this occurs, as the Hydra roars and changes colour. At the start of each phase, the Hydra will perform three auto-attacks before performing a special attack.
The Hydra attacks with both Magic and Ranged. The Hydra will begin the fight with either combat style.
Guide, gear, inventory, locations, pictures and money making rates from the OSRS Wiki (CC BY-NC-SA 3.0).