Unicorn
Description:
These legendary, horned horses are extremely rare. They are typically not aggressive, but will avoid humanoids at all costs as they are relentlessly hunted by ruthless poachers looking to take their horns as trophies.
In fact, myths and legends abound relating to the uses of unicorn horn. Some say a unicorn horn can resurrect the dead, others that it can be forged into a spear that will slay a god, still others say if blown as a horn it can stop time. While the theories are countless, the number of people who have every even seen a unicorn is vanishingly small.
Another reason unicorns avoid humanoids, is that their are perversely wealthy and immoral indviduals who seek to capture a unicorn to be broken in as a steed. Ancient legends of heroic champions taking unicorns as mounts are probably notning more than myths - and in any case, the cruel and wicked nobles who send entire armies into the woods in search of a single unicorn may have missed the morals of these myths; that the virtuous riders of these creatures are always of the purest heart; capturing and enslaving a unicorn to serve as a mount seems to be missing the point entirely.
Whether broken and forced to serve as a mount, or willingly in service as a mount to someone of pure heart and virtuous intent, a unicorn cannot be trained to ride into mounted combat. A unicorn will carry a rider, but will not carry a load on its back.