What about Str 23, Dex 14, Con 21, Int 6, Wis 13, Cha 10?
Aelian said:"I have learned that in India are born Wild Asses (Onoi) as big as horses. All their body is white except for the head, which approaches purple, while their eyes give off a dark blue colour. They have a horn on their forehead as much as a cubit and half long; the lower part of the horn is white, the upper part is crimson, while the middle is jet-black. From these variegated horns, I am told, the Indians drink, but not all, only the most eminent Indians, and round them at intervals they lay rings of gold, as though they were decorating a beautiful arm of a statue with bracelets. And they say that a man who has drunk from this horn knows not, and is free from, incurable diseases: he will never be seized with convulsions nor with the sacred sickness (epilepsy), as it is called, nor be destroyed by poisons. Moreover if he had previously drunk some deadly stuff, he vomits it up and is restored to health.
It is believed that Asses, both the tame and the wild kind, all the world over and all other beasts with uncloven hoofs are without knucklebones and without gall in the liver; whereas those horned Asses of India, Ktesias says, have knucklebones and are not without gall. Their knucklebones are said to be black, and if ground down are black inside as well. And these animals are far swifter than any ass or even than any horse or any deer. They begin to run, it is true at a gentle pace, but gradually gather strength until to pursue them is, in the language of poetry, to chase the unattainable.
When the dam gives birth and leads her new-born colts about, the sires herd with, and look after, them. And these Asses frequent the most desolate plains in India. So when the Indians go to hunt them, the Asses allow their colts, still tender and young, to pasture in their rear, while they themselves fight on their behalf and join battle with the horsemen and strike them with their horns. Now the strength of these horns is such that nothing can withstand their blows, but everything gives way and snaps or, it may be, is shattered and rendered useless. They have in the past even struck at the ribs of a horse, ripped it open, and disembowelled it. For that reason the horsemen dread coming to close quarters with them, since the penalty for so doing is a most lamentable death, and both they and their horses are killed. They can kick fearfully too. Moreover their bite goes so deep that they tear away everything that they have grasped. A full-grown Ass one would never capture alive: they are shot with javelins and arrows, and when dead the Indians strip them of their horns, which, as I said, they decorate. But the flesh of Indian Asses is uneatable, the reason being that it is naturally exceedingly bitter."
Ctesias said:"In India there are wild asses [the Monokerata or Unicorns] as large as horses, or even larger. Their body is white, their head dark red, their eyes bluish, and they have a horn in their forehead about a cubit in length. The lower part of the horn, for about two palms distance from the forehead, is quite white, the middle is black, the upper part, which terminates in a point, is a very flaming red. Those who drink out of cups made from it are proof against convulsions, epilepsy, and even poison, provided that before or after having taken it they drink some wine or water or other liquid out of these cups. The domestic and wild asses of other countries and all other solid-hoofed animals have neither huckle-bones nor gall-bladder, whereas the Indian asses have both. Their huckle-bone is the most beautiful that I have seen, like that of the ox in size and appearance; it is as heavy as lead and of the colour of cinnabar all through. These animals are very strong and swift; neither the horse nor any other animal can overtake them. At first they run slowly, but the longer they run their pace increases wonderfully, and becomes faster and faster. There is only one way of catching them. When they take their young to feed, if they are surrounded by a large number of horsemen, being unwilling to abandon their foals, they show fight, butt with their horns, kick, bite, and kill many men and horses. They are at last taken, after they have been pierced with arrows and spears; for it is impossible to capture them alive. Their flesh is too bitter to eat, and they are only hunted for the sake of the horns and huckle-bones."
I'm ok with a slightly higher AC. Unicorns at the same size and only 4HD have AC 18.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.