Phased out once you complete the "Theramore's Fall" scenario. Speak to Zidormi to access the pre-destruction phase. Originally this hydra just came in black. The orange variant was introduced in Patch 7.1.
Level scaling: In Shadowlands most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.