The first time I came across this particular pokémon I didn't think it was "real." I distinctly remember (because it was two months ago), I was sitting on my brother's couch reviewing his old (i.e., worthless) pokémon trading cards with my four year old nephew. My nephew pulled it out of the stack to show me.
"What's this one, Uncle Willy?" he asked.
"I don't know, I've never seen that one before."
Seriously. I thought it was some kind of aberration. A pokémon that had to have been made up only for the trading card game. I took the time to look this guy up on Bulbapedia and was surprised to see that he had been introduced in Generation II. I had played Pokémon Gold!
The second time I saw this guy was in the anime episode "Some Like it Hot." Really? an entire episode devoted to this most forgettable of pokémon? He's so bad I even forgot he existed at all!? Geez. That episode didn't even have particularly good plot. An oversized one was blocking the path Ash, Brock, and Misty were taking so they needed someone to capture it. There you go.
Oh well - since we are done covering all of the 600+ level competitive pokémon, it's time for a palette cleanser - Magcargo.
At first I thought Magcargo was a "transportation" pokémon. It had cargo in it's name and carried a rock shell on its back! With a little thought, though, I realized that the emphasis is on the final syllable. Just like escargot, Magcargo is just a fancy snail. Please don't try to eat one, though, you'll burn your tongue!
I do like a unique pokémon and Magcargo has a little of that going for him - he's the only Fire/Rock-type of all the monsters. What does that really get you? Well, he's extra extra weak to Ground and Water attacks and he does't do very well with Fighting and Rock moves. No immunities but, intriguingly, he does have resistance to Normal, Flying, and Bug type moves which may help you out in the right circumstances.
Magcargo gives you the choice of three abilities: Magma Armor, Flame Body, and Weak Armor. Personal bias - I don't like Weak Armor. Anything that lowers the Defense stat to raise the Speed stat is a bit suspect in my opinion. Keep in mind, though, that of all his stats, Magcargo's Defense is highest (matches Cresselia's), so Weak Armor may not be so bad. Magma Armor and Flame Body both help you hatch eggs more quickly. Out of those two, I prefer Flame Body (chance of burning an opponent who touches you) over Magma Armor (you can't be frozen). I just feel the number of competitors out there who are trying to freeze people isn't huge.
Sadly, although Magcargo is fully evolved, his base stat total (410) put him squarely in with intermediate evolutions such as Pupitar, Gabite, and Fraxure.
Grow your Magcargo defensively. If you're working with Weak Armor, try for a Bold Magcargo, Attack is his weakest stat so it won't hurt too much to mine that while building up Defense. Magcargo also learns more special attacks than physical attacks. While EV training, distribute across HP, Defense, and Speed and you may be able to pull off some neat tricks.
Give your Magcargo Flamethrower for its Fire-type attack and Ancient Power for its Rock-type attack. While Ancient Power isn't the strongest Rock-type move, there is a chance that all of Magcargo's stats could be raised one stage. Would you look at that - Magcargo has this sneaky way of starting out underpowered and then growing more powerful as battle goes on. Not guaranteed, but something to think about. Earth Power is a powerful Ground-type move to diversify Magcargo's set (still a special attack to leverage that stat). Finally, try include Reflect to leverage that high Defense stat.
Magcargo can hold Light Clay to extend the length of Reflect. If you are thinking of building a speedy Magcargo give him the Choice Scarf and pound away at your opponents with Ancient Power.
When facing a Magcargo, get out your Fighting-type and use Brick Break. It is a sufficiently diversely available move and will knock out Magcargo's Defensive capabilities.
Remember, snails are for snuggling, not for eating!