If I remember correctly, you get a letter on Father's Day revealing your dad is a bull.

It's a disguise so they don't know he is human

I always thought it was a hat

Later episodes have the round, horned hat as one of the few available shapes for custom hats.

Like the girl is wearing something that looks like a medieval princess's hat, I think he's just supposed to wear a "viking" hat (the historically inaccurate but popular costume kind).

I'm pretty sure they just wanted :

_ No free hair because not enough polygons to make them look good (don't forget AC for Gamecube is really a slightly augmented N64 game)

_ designs that evoke "imaginative kids that love to play pretend" to you.

The boring choice would have been baseball cap, like any other cliche 90s kid character design.

They're trying to brainwash your kids to worship Satan.

(/s)

Bottom kind of looks like cow ears.

I like to believe that his name is Logan or Patch and he has left superheroing behind for a simpler, quieter life.

Cowlicks? I can't remember what YT video explained a good reason for it.

There is this but I think it just raises more questions

Maybe the female character is half horse.

Maybe the female has udders. 🤔