leonardoiscool
Ah, I see.
I don't think the mobs hitbox will have anything to do with preventing fall damage, I also thought the ender dragons hitbox would be replaced with the one set in blockbench, this is probably something you'd have to suggest or look into other plugins for, as I see no current way to prevent fall damage with a flying mob.
Now if the hitbox is replaced by the one in blockbench like I mentioned, you could always set the mob to one that already doesn't have fall damage such as the iron golem, or if the default hitbox actually is an issue, then a cat.
You can read up here to ensure your hitbox is done correctly.
https://itemsadder.devs.beer/plugin-usage/adding-content/mobs/advanced-method/hitbox
A few questions.
Does this entity spawn in and immediately die of fall damage? Or do you just mean in general, it is able to be killed by fall damage.
Also maybe explain the "weird movements" more, they should only move how you animated them in blockbench.
Are you able to mount the entity at all, or no?