Luxray should be Electric-Dark. Don’t believe me? Look at its eyes and its mane
Lucario should be Fighting-Psychic. Auras are pretty much their whole thing…
Gyarados should be Water-Dragon. It’s serpentine looks and yeah, do i need to go any further?
Serperior should be Grass-Dragon for the same reason as Gyarados
Milotic should be Water-Fairy or Water-Dragon type simply because of its beauty and again serpentine look
Psyduck should be Water-Psychic because… I think you can work it out
Flygon should be a Bug-Dragon (its in the name)
Dunsparce should be Normal-Ground
Charizard should be Fire-Dragon