So i play the game on switch with save states the second when mario says fight, and i keep getting the exact same kind of fight, like in king hippo i get a block and 4 mouth opens. Or on mr dream where after the 4th and 7 th gravedigger he does the 8 second delay, so im thinking that the rng can be manipulated like the hippo manippo

save states save the RNG/frame rule, everything at the point you make the save.

What Pap said. Save states don't exactly manipulate the game, it just has the side effect of saving everything to that point, so the next rng in the game will happen every single time you load the state. This also applies to SPO and probably PO Wii. (Note: because of this, save states aren't as reliable as you may think, and you shouldn't use them outside of practice. But even then, it can limit your experience practicing because with MTPO, if you want to seriously speed run the game, you need to able to play through all possible situations the game's rng can throw at you.)

When I use save states, I save at the fight screen. Then I can delay pressing start to get different RNG patterns when I practice a fight.