If You Wanna make up the last gym of ruby or sapphire then just take your default Pokemon and level it upto 65 to 70 lv then take kyogre and rayquaaza on the second and then the most powerful Pokemon you have.
With the seventh badge in Pokemon Ruby version, you can control caught or traded Pokemon up to level 70.
Mossdeep cityit is in mossdeep
journey again to achieve the another battle called the 8th gym Pokemon ruby
In Pokemon Sapphire, Ruby and Emerald the 7th Gym that's located in Mossdeep City has Psychic type Pokemon.
physic type pokemon.
Use strong water or dark type Pokemon
no
Steel is super effective against rock type pokemon.
umm i dont know
protect
Swellow Salamence
Water-type Pokemon are weak against Grass and Electric-type moves.