Take a mixed bag of Lvl50+ Pokemon.Water types work best and fighting and poison types would be screwed if you bring them out.
Twins Liza and Tate in Moss deep City, they use physicic Pokemon
Steven stone lives in mossdeep. go to his house ( the one at the northwestern part of the island) and he will give it to you. BUT you need to beat liza and tate, the city's gym leaders, to use it.
You get the abilty to use the move Dive from Tate and Liza in Mossdeep and then you can teach your Pokemon to Dive! X3 POKEMON-1001
From Steven at his home in Mossdeep City but you can't use it until you've defeated Tate and Liza, the Pyshic Pokemon Gym Leaders :)
When they use Solrock and Lunatune, a Water Pokemon with good Special Attack and Surf would be a great help. Also a Dark-Type (Against all) and an Electric-Type (Xatu) would give you a real boost. If you don't have that, they would be a real challenge. Just play with the weaknesses and figure out when its wisest to use those of your Pokemon that has the best Special Defense stat, since they mostly use Special Attacks.
The sixth gym leader is called Tate and Liza, a pair of physic type trainers. They use a Solrock and a Lunatone, both rock and physic type.
simple you go to mossdeep city vis surf beat tate and liza then help steven beat team magma in the space place at the northeast of the city and then go into all houses until you reach Stevens house and use dive to find the seafloor cavern and beat team aqua
If you want to beat them first of all its a double battle.second i think that the only a Pokemon they have is that sun Pokemon and that moon Pokemon's the moon Pokemon and sun Pokemon are rock type and physic types using a grass,steel,ghost,dark and ground but maybe it has an ability to dodge all ground-type moves no matter what. If they have more Pokemon they are physic. Use dark,ghost or bug type Pokemon would be suitable.
Tate and Liza the Mossdeep Gym Leaders use Psychic-type Pokemon so the best option to use would be either Dark-type Pokemon or Ghost-type Pokemon however Bug-type Pokemon will work as well additionally Steel-type Pokemon have a resistance against Psychic attacks and Steel-type attacks are super effective against Pokemon that are part Rock-type which Lunatone and Solrock are.
beat the Pokemon league and beat N and you use your Master Ball to catch him
use psychic Pokemon and beat all the trainers to get more light
if you have a swampert,use it against lunatone and solrock.try to find a dark type Pokemon and train it to around level 40.it will be a big help