OK, forgive me boasting, but it's so rare I actually manage to pull off a decent strategy 
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Pokemon Colosseum, Under Colosseum Double Battle
Battle 3 - Guy Baben.
Has a Lombre, Muk, Sunflora, Mantine, Glalie & Forretress. All level 50.
In Double Battle you pick 4 pkmn from your team of 6. Looking at the possibilities from his team, I picked Magneton, Nidoqueen, Charizard and Blastoise. (Although my Blastoise didn't actually see any of the battle.)
He started with Mantine and Forretress, I started with Magneton and Nidoqueen.
1. My Magneton used Thunderbolt to 1 hit KO the Mantine (4 x vulnerable to Electric) before it was able to move. He sent out Lombre to replace it.
2. His Forretress used Dig, which I figured was probably aimed at my Magneton. So I did a defensive switch to Charizard.
3. With my Magneton safely out of the way, my Nidoqueen used Earthquake - for double damage to the Forretress that was still underground, and harmless to my part-Flying Charizard. Took the Forretress down to 3 HP (!).
4. His Lombre used Leech Seed on my Charizard. Whoopie do. His Forretress came out of the ground to do no damage to my Charizard. Oops.
5. My Nidoqueen used a second Earthquake, to finish off the Forretress and also damage the Lombre quite a bit more. He sent out his last pkmn, Sunflora.
6. My Charizard used Wing Attack to finish off the Lombre.
7. Finally, a Double-Edge from Nidoqueen and a Flamethrower from Charizard knocked out the Sunflora before it could even move. Heh.
So yeah, I'm sure someone will think of something they'd have done better, but unlike the GBA games where you can find out exactly what team the opponent has, because you only choose 3 or 4 from 6 in Colosseum, it's never possible to predict exactly what they'll do. (I've done the same battle 3 times in a row sending out the same 4 pkmn, and seen 5 or 6 of the opponent's). So I was pleased, anyway.
.Pokemon Colosseum, Under Colosseum Double Battle
Battle 3 - Guy Baben.
Has a Lombre, Muk, Sunflora, Mantine, Glalie & Forretress. All level 50.
In Double Battle you pick 4 pkmn from your team of 6. Looking at the possibilities from his team, I picked Magneton, Nidoqueen, Charizard and Blastoise. (Although my Blastoise didn't actually see any of the battle.)
He started with Mantine and Forretress, I started with Magneton and Nidoqueen.
1. My Magneton used Thunderbolt to 1 hit KO the Mantine (4 x vulnerable to Electric) before it was able to move. He sent out Lombre to replace it.
2. His Forretress used Dig, which I figured was probably aimed at my Magneton. So I did a defensive switch to Charizard.
3. With my Magneton safely out of the way, my Nidoqueen used Earthquake - for double damage to the Forretress that was still underground, and harmless to my part-Flying Charizard. Took the Forretress down to 3 HP (!).
4. His Lombre used Leech Seed on my Charizard. Whoopie do. His Forretress came out of the ground to do no damage to my Charizard. Oops.
5. My Nidoqueen used a second Earthquake, to finish off the Forretress and also damage the Lombre quite a bit more. He sent out his last pkmn, Sunflora.
6. My Charizard used Wing Attack to finish off the Lombre.
7. Finally, a Double-Edge from Nidoqueen and a Flamethrower from Charizard knocked out the Sunflora before it could even move. Heh
.So yeah, I'm sure someone will think of something they'd have done better, but unlike the GBA games where you can find out exactly what team the opponent has, because you only choose 3 or 4 from 6 in Colosseum, it's never possible to predict exactly what they'll do. (I've done the same battle 3 times in a row sending out the same 4 pkmn, and seen 5 or 6 of the opponent's). So I was pleased, anyway.