The Elite Four

A recomendation for the Pokémons you should have is this: Pikachu (or another electric type), Gyrados (or another aquatic type), Haunter (a ghost), Articuno (one ice type), Charizard (a fire one), and another weak (To allow it to gain a lot of XP. If I definitely want to win I take either Blastoise or Venusaur. Usually Venusaur because Blastoise kinda just stands there if Gyrados is on).

1) Lorelei
Dewgong
Cloyster
Slowbro
Jynx
Lapras

Here is how I defeated them. Dewgong: One hit with Thunder. Cloyster: One hit with Thunder. Slowbro: One hit with Thunder. Jynx: Put to sleep with Haunter, then constant Dream Eater. Lapras: Two hits with Thunderbolt. Oh, in case you couldn't tell, the electric attacks were by Pikachu :)

2) Bruno

Onix
HitmonChan
HitmonLee
Onix
Machamp

Here's my way: Both Onixes are killed in one hit by Surf from Gyrados. The rest are put to sleep by Haunter and Dream Eater kills them all with one hit.

3) Agatha

Gengar
Golbat
Haunter
Arbok
Gengar LVL 60 Uses Psychic!

This is a tough match. I started with Pikachu and hit Thunder on Gengar. He then usually uses Substitute, so a Thunderbolt cancels it out. It's best to use
Articuno and do either Ice Beam or Blizzard on him, it beats him fast. Sometimes she drags Gengar out and sends in Golbat. Golbat and Arbok were easily beaten by my Haunter (Hypnosis, Dream Eater twice). The ghosts can be whupped by Articuno's ice and Pikachu's electricity. But the last Gengar is really hard.

4) Lance

Gyrados
Dragonair
Dragonair
Aerodactyl
Dragonite

Lance's dragons are not actually that hard. Even Thunderbolt from Pikachu kills Gyrados in one hit. Articuno's ice beam kills both Dragonairs in one hit. Pikachu's thunder kills Aerodactyl in one hit. Dragonite can be tough.... until he's put to sleep by Haunter :)

5) Gary Oak (Rival)

I still do not know if Gary changes his Pokémon depending on what Eevee he ends
up with, but here is how I beat the team he uses:

Sandslash
Alkazam
Magneton
Exeggutor
Cloyster
Flareon

Sandslash is beaten with one Surf from Gyrados. Alkazam I usually beat with Articuno, one or two Blizzards should do it. Magneton I always find hard to beat for some reason, use Pikachu against him to cencel out his attacks perhaps, but then again so are yours. I usually just go to my backup plan, Haunter. Exeggutor burns well :) One or Two Flamethrowers. Cloyster fails to remember what happened to Lorelei's and gets Thunder between the eyes. Finally, Gary's "best Pokémon,"Flareon, comes in..... and gets Surf twice and is kaput.

Thanks to the Psychic Pokémon Connection by the Info