I recently completed pokemon Y (Like, a few hours ago) and well, I managed to find a super effective (See what I did there?) strategy, that is especially useful when battling the Elite Four/Champion as I discovered myself.
1. Revive and Restore
What you need:
* Revives or Full Revives
* Full restore/Max potions
Ever in the middle of a battle and the pokemon you need to murder the opposing pokemon is dead or your in a battle with 1 or two pokemon left? This method is sure to help you out.
Step 1. Make sure you have a pokemon out.
Step 2. On your turn's make sure to either:
* Heal your active pokemon so it doesn't die.
* Revive one of your pokemon.
(Or heal one of your recently-revived pokemon if your using Revives instead of Max Revives)
Step 3. Repeat the above steps intil you have revived all your pokemon and healed them up.
Step 4. Win.
Warnings:
Sometimes, a Pokémon might land a critical hit. If your in the Pokemon League, your current Pokémon is probably gonna faint. Swap to another Pokémon and continue where you left off.
Tips:
Steelix was a good pokemon for me, but if your fighting a fire Pokémon, it might not be a good idea.
(You can get a Steelix from this guy in a Pokémon centre in return for a Luvdisc)