Sweeping waters: Gyarados, Feraligatr, Starmie.
Bulky waters: Milotic, Slowbro, Suicune, Swampert, Blastoise, Empoleon, Vaporeon and many more.
As for fire types, it depends on what you want it for. In Emerald, I wouldn't suggest using a fire type in the Frontier 'coz most fires seriously lack the versatility a good Pokémon needs in the Frontier.
About your team now. A Sceptile used in the Frontier has to be an all-out special sweeper, period. Go for the classic 3rd gen set:
Sceptile @ Petaya Berry/Scope Lens
Timid, 252 SpAtk, 252 Speed, 6 HP
- Leaf Blade
- Thunderpunch
- Dragon Claw
- Crunch
As for Milotic, what ExplorerAce said.
Latias now. In my Emerald, I had been using my Latias a lot. The set I'd suggest is:
Latias @ Leftovers (Shell Bell if there's another Leftovers holding Pokémon)
Rash (not the best nature but you can't change it after all), 252 HP, 252 Speed, 6 SpAtk
- Calm Mind
- Ice Beam
- Thunderbolt
- Psychic
About Hypnosis on Milotic,
http://www.legendarypokemon.net/pokedex/...c/breeding
Be sure to check our Pokédex about other Pokémon too.