The Unicorn Mount is summoned by the Blessed Apple, which is dropped by creatures in the Hallow (Fairy confirmed). The unicorn mount can double jump and speed up as if it had Hermes Boots, Spectre Boots, etc. , but is much faster than both. Sparkles scatter from behind the unicorn as it runs. Running into an enemy at full speed will damage the enemy. (Damage Range needs confirmation)
This mount is fast enough to outrun most (non-enraged) bosses, including the Moon Lord. It is a very effective mount for use of ranged weapons.
The Unicorn mount will not gain speed in mid-air, make sure to reach maximum speed before jumping (If possible)
Riding this mount while firing the Rainbow Gun unlocks the achievement "Rainbows and Unicorns". This is a direct reference to the Adult Swim game Rainbow Unicorn Attack.