Diababa is the first boss of the first dungeon, the Forest Temple, in Twilight Princess. The boss itself is made up of two large plant heads that resemble Deku Babas and one massive plant head with a hidden eye inside its mouth. The appearance hints Diababa may have originally been a Deku Baba which touched the Fused Shadow.
The beginning of the fight starts with only the two smaller heads. Bomblings are seen perched on logs floating in the water, and Link uses the Gale Boomerang to make them collide with each of the two heads. Each single hit defeats each one.
The second phase of the fight begins when the larger head bursts out the water. Ook then appears and swing across the room carrying Bomblings for Link to use to stun Diababa's middle head, leaving its eye (the critical point) open for Link to attack with his sword. Upon recovering, Diababa will spray poison at Link, so he must move quickly to dodge it. The two smaller heads will also continue to attack occasionally. Link dodges its attacks and repeats the process until Diababa is defeated.
Upon Diababa's defeat, Link receives the first of the three Fused Shadows and a Heart Container.