Marcello's gift allows him to immediately know whether a human or vampire has an extra gift; he'll be able to know how strong the gift will be and what type it will be. He does not need contact with the other person, he only needs to look at them and he'll know. Also, his gift is so strong that when he looks at a human, he can know every possible gift that his/her traits will produce when they become a vampire, but the strongest type of gift which will be manifested is the easiest for Marcello to identify. He is also able to identify if a Quileute will be a shape-shifter.