Y Limit Mob Spawn

This idea allows mobs like phantoms to spawn on certain Y location For example the player needs to be at Y 150 for phantoms to start to spawn Phantoms will still have their spawn effect where the player doesn't sleep the more commonly they spawn And from this idea might be good for the caves and cliffs update since the phantom is a flying hostile undead mob The phantom can spawn anywhere if only the player is at y 150 And also they won't despawn when the player steps below y 150 The phantoms will just chase the player But ofc phantoms will stop spawning because their at below the phantoms Y limit spawn And I think this idea might be a good thing for phantoms to be less of a annoying and tricky creatures And we'll the phantom membrane might need more use Or in other words the whole phantom needs newer and more bigger Value since elytras can be easily fixed with mending How about having able to craft elytras but with a expensive cost? But this are now outside of the topic So ye This feature will allow phantoms to lessly spawn on the surface unless the player is in a certain Y position