in his trading card he's said to be "shy, jumpy, nervous, good-hearted, and dorky" which he very much is. he appreciates loneliness from time to time but also likes hanging out with people who're energetic as they often help him be more positive. he's quiet most of the time but can still talk without a mouth, can kiss just as well too. he presumingly talks through telepathy
he likes reading comics, playing board games, attending cons and in general has very nerdy hobbies. while he freely indulges in those things with zoe, he's still insecure about his interests as he's worried about other people finding them boring. another thing he likes doing is going on adventures with his friends as long as they're not too wild or mean
he's aware of how shy he is and wants to improve himself, his date dialogue in monster roadtrip's oz + amira dlc is him brainstorming ways to become 20% cooler (HIS WORDS not mine!). he stutters, questions himself and tries to calm his nerves a lot during his ingame voice lines, specifically at the beginning of his rounds. he can also get a bit pessimistic on his own. to put it simply, oz is very socially anxious
and fun fact, he's the physical embodiment of fear! in monster roadtrip's mirror event he's said to be a vessel for something that's only called "oz's fear", a vessel that's apparently showing cracks... anyway! he's an ancient entity older than time itself. why was he going to spooky academy? no clue
the blobs on him are called phobias and also represent.. well. different phobias. if you stare at them closely they can look like "the most terrible, fucked-up fears you could imagine", but ultimately oz thinks they're really cute. in the oz + amira dlc for monster roadtrip, oz talks about how he doesn't know how they showed up. he sometimes thinks they're a coping mechanism he subconsciously created to feel less alone
they have a lot of personality even if they don't speak and act completely independently from oz. when oz goes to the bathroom in monster prom (this is normal don't worry about it), they style his hair on their own which gets him nervous. they're also very proud of it too! they're silly but very loveable. in monster camp they're a drink you can have called phobia shots, but i highly doubt that they're safe for consumption. they do increase boldness though
oz's name comes from a fan who named 'yellow' oz during the prerelease of the first game, he's one of the only characters with no last name. his design was also very much inspired by death in aidosaur's death and cecilia