My idea is an Enderwolf the black/dark alternative to the ones in the overworld. These creatures spawn in the End only when the dragon is killed. They are tamed with a single bone of ender (read more about this below) While trying to tame it, you must look at it's white eyes the whole time and give him the bone. Once tame the wolf will just stay motionary. If you right click it with your fist nothing will happen but when you use the same empty slot anywere else that isnt usable (Chest, crafting table, furnace, etc) the enderdog teleports right onto the location. The only time the ender wolf moves on its own is when there are hostile or pigmen around you. The enderdog does not attack endermen or other wolfs and endermen will allow you to stare at them.
Enderdogs and wolf have 15 full hearts and do 5 hearts of damage
The bone of ender is crafted by 3 eyes of ender in a straight horizontal line