Most of these headcanons will be used in "The Story Of A Mage"

Hyness and Max Haltmann are his dads, making Susie his half sister

Transmasc

Cat

His magic is very strong, practically uncontested, thanks to the lingering power of the Crown boosting it just a little, even then it was quite powerful before the Master Crown's influence

Sometimes gets sick, and throws up black ichor, and the occasional eye, it has to be clawed out

Ears are sensitive

Too much use of magic causes the "Crown Sickness" to flare up, which drains his magic further

Covered in soft fur

Ran away from the Jamba cult at a young age

He was about 17 during the KRTD incident

Spent way too much time in Another Dimension, it drove him mad

Had a hard time readjusting to society when he got out and ended up in SKC

Ran a pretty good shop, the prices were only slightly high

Eventually, the Lor Starcutter came and got him, taking him out of SKC

Everyone panicked when he came back, but Kirby was mostly relieved, he felt really bad about the fact he basically killed him

Marx nearly killed him when he returned, then they kissed and all was good

Merry Magoland is doing very well and is very fun (There is an entry fee)

Never put anything on his head, he will kill you