Nyxborn Unicorn is a common Enchantment Creature — Unicorn card from Modern Horizons 3 (MH3), collector number 37. Current market price: $0.21 (foil $0.27), TCGplayer market prices via Scryfall.
Bestow {3}{W} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached.) Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.) Enchanted creature gets +2/+2 and has mentor.