Is this item supposed to be this horrible? Engraved Aerakyn Horn It is supposed to increase ability damage by 100% for 8 seconds. If the target doesn't die, then either you die or your damage is reduced (almost always die). Testing it on a dummy using Lifetap, which does constant damage, there is approximately a 10% increase in damage... I wouldn't expect damage to actually double, but considering it almost always kills you, this is a ridiculous risk vs reward item.
It increase your ability mod but not the 50% cap in ab, mod for each spell. With ToV gears, pretty much every classes can cap its ability mod, so this item is useless except maybe for Sorcerers.