This pet was available only after Epic VI: Resurrection update
The Unicorn is a pet based on support, it has a healing skill, damage+debuff skill and 2 buffs. After making this pet evo3 you will be able to mount it.
For a better health build use (Int/Wisd + Vit stones) Gear: ( Warrior armour + 2h Mace- note that it will not gain 12% max mp as it has no passive for warrior armour)
For best Blinding effect use (Wis + Int) gear: (Devoted Magician Armour + Devoted 2-Handed Staff) [More likely build for a pet class DS]