He used to date Juliet, a vampire, and Justin Russo's ex-girlfriend.
Mason Greyback is played by Gregg Sulkin. Mason is first mentioned in Season 2 episode Future Harper when Future Harper tells Alex that she seems irritable and asks if she broke up with Mason yet, implying that she will date a boy named Mason in the future. Mason is first fully introduced as a student in Alex's art class. They begin to date in Alex Charms a Boy. They both love to paint, but Mason loves painting pictures of dogs on human bodies from American history. Alex puts a spell on him to make him obsessed with painting her. The spell is lifted, though. He gives her a necklace that lights up when the wearer is in love with the person who put it on them. In Wizards vs Werewolves it is revealed that he in fact is a werewolf. He doesn't turn Alex into a werewolf when they kiss, because he is a purebred and only mutts turn people into werewolves when they kiss. He helps in search for Juliet after picking up her scent from her dental floss. He leads them to the mummy's tomb where they rescue her. It is revealed that he and Juliet used to date (which also reveals Mason doesn't age) and he admits he never stopped loving her, which breaks Alex's heart. She throws away the heart necklace he gave her. He tries to prove his love for her by going back to the mummy's tomb to find the necklace. Justin, Max, and Juliet come to rescue Alex. Max likes Mason, but Justin hates him for breaking Alex's heart. When Justin tries to make Alex leave the tomb, Mason turns into a werewolf, and starts fighting Justin and Juliet. He is attacking Justin when Juliet bites him, causing him to turn into a wolf permanently. Before his transformation, Alex puts the necklace on him and it lights up. Alex knows now that he truly loves her, but he leaves because as a wolf, he has no control. He leaves the mummy's tomb as he transforms into a wolf. It is a known fun-fact that his last name references to Harry Potter villain Fenrir Greyback, who is also a werewolf. In Wizards Unleashed, it is discovered that Mason has been captured by wizards and being used in TV advertisements. Upon discovering this, Alex manages to retrieve him, and uses magic to revert the transformation, but only succeeds in leaving him with pointy ears, claws, and mass abounds of fur. Though Alex initially has trouble accepting Mason in this new state, she eventually gets over it and Justin manages to fully restore his humanity by playing a magical jawharp at the end of the episode. Despite rumors, Mason will not be a main character in Season 4, but will appear in few episodes. In Wizards Exposed, the wizards get caught, and Mason gets caught while he was "admiring his hat." In Season 4 Episode 2, Alex Gives Up, they are forced to break up due to a rule that says that werewolves and non-wizards cannot date because the werewolf always ends up eating the human due to their anger management issues. At first, Chancellor Rootie Tootie Tootie appealed the rule, but then Alex, jealous of Lisa Cucuy, who was hitting on Mason, and makes Mason extremely angry by embarrassing him in front of her brother, her parents, and the Cucuy's. Mason then transforms into his half-werewolf form and Chancellor Tootie Tootie, seeing he is incapable of controlling his anger, takes back his appeal, therefore forcing Alex and Mason to break up. In "Journey to the Center of Mason", Mason eats Dean Moriarty (Alex's ex-boyfriend; they broke up when Dean had to move to Ohio) because he is jealous that Alex is spending time with Dean and not him. Alex, Justin, and Max go inside of Mason. While in Mason, Alex,Justin, and Max go into his brain. Alex sees that all Mason does is think about her.When Alex, Justin, and Max come out of him with Dean, Dean leaves because Alex doesn't want him back. After he leaves, Alex and Mason get back together because Alex decided to rejoin the Wizard Competition so she and Mason could be together. In the episode, Dean only refers to Mason as "London Bridges". Mason has the deepest love for Alex and has nicknamed her 'Brown Eyes', 'Little Meatball', and 'Love'.