mew. he can learn any TM or hm
Gothita is a Psychic type pokemon.
By batteling them against ghost type Pokemon
Cosmog is a Psychic type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Regardless of their type, Pokemon can learn a variety of moves and attacks, so, Psychic is not immune to any Pokemon. If you are referring to what "type" has no effect against Psychic, the answer is none. Psychic isn't immune to any type. It is resistant to Fighting and Psychic attacks though. There is one thing, however, back in Pokemon Blue, Red and Yellow, Psychic used to be immune to Ghosts, but that was years ago and strangely, after those 3 games, Psychic became weak to Ghost.
Munna is a Psychic type pokemon.
almost all of the water type Pokemon can learn and use waterfall
Gallade, but he is psychic fighting type.
Most water type Pokemon can learn the move Waterfall.
Most electric type and psychic type pokemon can learn flash.
Lugia and articuno
Gothita is a Psychic type pokemon.
Psychic type Pokemon are weak to Dark, Bug and Ghost type moves. Psychic Pokemon can also struggle against Steel types as not all Psychic Pokemon can learn moves effective against them. Overall the best type to use against Psychic types is the Dark type. Since the Dark type is not only super effective against them but is also immune to Psychic moves.
By batteling them against ghost type Pokemon
Cosmog is a Psychic type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Very badly worded question, I'd interpret it as "Why can't any of my Pokemon learn waterfall?". To answer the question, the most likely reason is that you don't have any water type pokemon. The great majority of water types are able to learn Waterfall through the HM obtained ingame.
psychic type pokemon are weak against psychic steel and dark
Pikachu can. Any grass or electric Pokemon may learn it.