Time for a tourney gamer opinion:

The best Pokemon in the game is Ninjask. Ninjask with Baton Pass and Substitute (holding leftovers).

Way this works: Ninjask is your frontrunner Pokemon. As the fastest in the game nothing will stop him from subsituting. He substitutes and your opponent kills the substitute. Your speed boost gives you an extra stat boost to your speed. You repeat this twice, leftovers restoring your HP some in between leaving you with a +2 (50% increase) to base speed and over half your HP.

You baton pass to the Pokemon best suited to kill your opponent, and you have the fastest and strongest Pokemon in the game. A great way to use this is with a Pokemon who has a 100% Sleep move like Breloom. You're always fastest so you'll always sleep first, you then substitute to guard, and Focus Punch or Rock Slide your opponent into oblivion. This can also be done with a special Pokemon nuke like Jolteon with Thunderbolt and HP Ice who can sweep a whole team. Or a superpowerful physical like Metagross with a good Meteor Mash and maybe a swords dance.

The only disadvantage to this strategy is enemies with Quick Attack, but you'll still get off at least 1 speed boost and still be able to rape any opposing team. I have some other favorite strategies too if anyone is interested in some other tourney strats.

Must you be so awesome Naznatips?

One of my favorites is Milotic ( Leftovers + Aqua Ring + Recover ); Ninjask is excellent as Naznatips said, and paired with a powerful beater like Slaking is unstoppable.

Blissey is very good as well but in many cases banned like the legendaries. And I like Shuckle too.

@Zap~

Nevermind I saw your signature and added you. So, one of my Pichus for Spheal?

@naznatips:

Those kind of strategies are not banned on tourneys? lol

And Salamence is on lots of teams because it's the second ranked non-legendary in terms of base stats averages, second to Slaking. It also has Intimidate which makes up a bit for it's lack of defense.

How to make an ultimate weapon: Want the fastest and strongest Pokemon ever? You need Poliwrath. This strategy is called Beliwrath, and here's how it works.

Poliwrath needs a moveset of Belly Drum, Substitute, Brick Break, and either Rock Slide or HP Ghost (I prefer ghost personally). He must be holding a salac berry. Your HP also needs to be divisible by 4 (this can be done by adjusting EVs).

Poliwrath needs to be switched in on an enemy water Pokemon who you know has nothing but water and ice moves while your enemy is using a water or ice attack. Water Absorb will mean you take no damage to a surf or other powerful water attack and 4X Ice Resistance will be practically no damage.

Your enemy will switch out (they'll have no choice) while you use substitute. Your enemy's next Pokemon will be supereffective against you, and while they attack you you will use bellydrum, taking away 50% of your max HP in addition to the 25% already lost by using substitute. This maximizes your attack power and automatically activates the salac berry boosting your speed to higher than nearly any Pokemon in the game. You suddenly have an extremely fast maxed attack Pokemon that can kill nearly anything except the super defensive waters in 1 hit.

Mewtwo is the most powerful pokemon of them all. Look at his stats.

vaporeon very strong water type, and acid armor plus its hp. very strong pokemon

Mine is now on my signature too i will add you when i'm at home

 @Naznatips Yeah Breloom Spore/Focus Punch/Substitute is great after a baton pass of +2 on Speed, but most of the great talent of Ninjask rises on the pokemon you baton pass its  status...so by itself ain't so great :P

If i use Ninjask i have a lot more fear to Ice Shard than Quick attack, you know it's low defenses/HP + weakness don't sounds so nice xD

It's fairly rare for an opponent to lead a Pokemon with Ice shard but fairly common for Quick Attack.  However, I lead an Ice Shard Weavile myself sometimes.  If my opponent has a dragon or Ninjask out they'll run away and I'll get in a swords dance.  Since I'm already ridiculously fast and have STAB on my Ice Punch and Night Slash I can often sweep a team with a single swords dance on Weavile.

Destiny Bond or Counter/Mirror Coat could really mess these tactics though :/