Nyxborn Unicorn — Modern Horizons 3 #37

Bestow (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.