i need help

Spiritomb- maybe your starter with good moves
Roserade- ice(froslass,abamasnow,ect.) flying(staraptor) fire(rapidash,infernape) psychic-(kadabra)
milotic (any electric type should work,grass is risky because of ice beam)
garchomp- I used giratina you could too because it has moderate defense
lucario is tough- it has shadow ball stone edge aura sphere and I think flash cannon so think either ground or fighting fire is risky
togekiss- used giratina (i think it's perfect for togekiss unless you own an electric type) ice and rock are risky because of aura sphere
you should have lvls 55-65 for a smoother ride
I got lucky with lvls 53ish but do not follow my example here
bring as much reveives possible with max potions,ect
I ran out and I bought 15!

Right the first one is spiritomb so use your strongest Pokemon to take it out for garchomp use a ice type Pokemon that knows ice beam or blizzard a few times and it should faint for milotic get a electric type Pokemon that knows thunderbolt or charge beam when roserade comes out use a fire type Pokemon with flamethrower or fire blast for lucario use a Pokemon that knows earthquake and last but not least togekiss use thunderbolt or chargebeam or thunder for togekiss.

Good luck beating cynthia.

Use dragon type.they atleast need 2 be in there 70s

You might need the most of help from Ice, Electric, and Fire type moves. It can be risky, but if the attack is strong against the Pokemon your against, it'll be a OHKO. The one thing you should worry about is Spiritomb, though. It has a good balance of Defense and Special Defense, but there is one way to take it down quickly. Have a Machamp, Machoke, or Lucario, and make sure it knows Foresight and a Fighting type move. That should easily finish off Spiritomb.