Dullahan/Headless horseman

Hostile & Friendly mob, The concept is this mob starts off hostile and will attack you if you come near it, however if you are capable of doing so, you can attach a jock-o-lantern to its "head" (or shoulders in this case) if this is done right, the headless horseman will now have a head and will become a friendly mob and will also follow the player that attached the jack-o-lantern to it, it would also be the only friendly mob that will actively follow you into the nether and or the End, therefore giving you an ally that you can rely upon even in the nether/End. The headless horseman would also be capable of being equipped with two different items, the first being a sword, the second is a lantern/torch/redstone torch, the idea behind this is that you can allow the horseman to act in specific ways, with the sword he will be aggressive towards hostile mobs and will actively attack them when in range, with the lantern/torch the horseman has an area effect that heals your health so long as you are in that area of effect, however this effect is at the expanse of the xp that you acquire from killing hostile mobs, so make sure to use it when it is really needed, I should also mention that these two items can also be unequipped from the horseman for the sake of negating these abilities when they are not needed. I hope this suggests was considerable is not entertaining for whom ever reads this.