>>19716080STAB would only apply once, like Hawlucha and Flying Press.
They way they code multi-typed moves is that a move has one type (Flying Press is Flying), and so gets STAB from Flying typed mons, but also factors in the Fighting type multiplicatively on top of the Flying type when it does calculations.
>>19716059Arceus would conversely be immune to Normal, Fight, Flying, Ground, Steel, Dragon, and Psychic, while only being weak to Rock.
Good ol' Rock.
