The Dahaka boss and true ending are only available if the player has obtained all nine Life Upgrades in the game and picked up the Water Sword from the Hourglass Chamber.
The Dahaka is an easy boss if you kill him when he grabs the platform's edge for the first time. If he is allowed to recover and jump back up, you might as well load a previous save because he is annoying as hell if allowed to enter his second or third phase of battle.
Use Slow-Mo (but try to have keep up 4 or 5 Sand Tanks full) to avoid his attacks and maintain a strong offensive. His tentacle attack can only be dodged easily if you roll sideways towards them when they shoot out his belly. Once 1/3 of his health is gone, Kaileena will use sand to blast him to the edge of the platform.
He usually stays on the ledge long enough for a player to get 2 or 3 Slow-Mo attack sessions in. But do not try to use Slow-Mo to finish him, you won't deal enough damage fast enough. Instead, try to get his health as slow as possible with 1 or 2 Slow-Mo attack sessions, and then finish him with Ravages of Time (Block+Amulet activation button).
If you are speedy about using Slow-Mo to reach the dangling Dahaka, and activate Ravages just before slow motion stops, you should be able to kill him easily (at least on Normal and Easy modes you will).
