Ender Serpent Mob

I assume the End will eventually get a makeover like the Nether has.

This mob functions as a sort of counterpart to the endermen.  While you have to avoid looking at endermen, you have to look at this entity every few minutes to prevent them from attacking you.  For the player's convenience, this timer only ticks down while the mob and the player can establish line of sight.  Retreating indoors pauses this timer, essentially.  They would make multiple audible warnings as this timer is about to run out as well.  When in a neutral state, they float very slowly through the air.  When attacking, they straighten their body and charge the player, similar to a phantom but moving in a straight line.  They'd also be angered when another of their kind is attacked by the player, like a zombified piglin but with less range.  They would deal less damage than endermen, as they're less of a threat, and would only have a bit more health than a player.  When in a neutral state their ambient noises should contribute to the atmosphere of the end.

I imagine them having a reptilian or arthropod-like design.  Making bane of arthropods more useful is always a good thing.  When killed, they'd drop a new type of meat that is of decent quality when cooked, like cooked salmon.  Should you prefer the arthropod route, this meat would be one segment in its segmented body.

As for size, they should be around as long from head to tip of the tail as a ravager.  Decently large.