Overview:
Now, before you go yelling "Gimmick!" as true as it may be, I have to say that I've had a lot of success with this and still frequently use it on my teams. (And it's caused many a rage-quit as well.)
The beauty that I find in Mawile is the fact that it's one of the only pokemon who you can actually abuse it's all-around low stats the best at level 100 as opposed to pokemon such as Aron or Rattata. This is due to the fact that an endured Metal Burst from Mawile hits like a truck considering it's HP. Dealing a whopping 454
set damage. OHKOing nearly any pokemon brave enough to let loose on the little fellow.
To give you an idea, Only Blissey, Chansey, and Wobuffet can survive an endured Metal Burst without investing in HP. All pokemon between 126 and 170 base HP must invest in the stat in order to survive, and everything base 125 HP and lower will always be OHKO'd no matter how much HP they invest in. Which, for the record just so happens to be exactly where Kyurem-B and Kyurem-W sit at.
Strategy:
That's the meat and potatoes of the moveset. Now onto actually utilizing it.
The object of the game is simple. Utilize Mawile to it's full potential by swapping it in after your pokemon has fainted. It's usually a good idea to scout with Protect with a turn, but in some cases it may be better to simply jump in with your Metal Burst. Your goal is to take as much damage as possible and turn it around to KO your opponent.
Mawile also proves to be an extremely effective anti-sweeper as well. An opponent that has boosted their attack level is likely to find it impossible to reliably ping Mawile enough to deactivate the Focus Sash, but at the same time not enough to get knocked out by a vicious Metal Burst. This forces them to choose between trading with Mawile, or swap out and lose their stat boosts. In either event, this will typically stop a sweeper dead in it's tracks. To that effect, this means Mawile is an immediate threat to many Ubers due to the high attack power that many of them are sporting.
Sucker Punch is an excellent move as well and it's utility is rather useful. It serves many purposes. First-off, after your initial Metal Burst, Mawile is pretty much spent. However, you can still do some ping damage to the next Pokemon with Sucker Punch. This has the added benefit of threatening Multiscale users and Sturdy or Focus Sash using pokemon. If you end up sending in Mawile on an opponent that just barely survives, you can knock them out and allow Mawile to live another day. Inversely, if they are packing Endure or Sturdy, Metal Burst first, then finish them off with a Sucker Punch to effectively bypass the endure. Even better if your opponent has threatening Pokemon that were brought back hanging by the skin of their teeth allowing you to potentially pick off more than one Pokemon at a time. Sucker Punch is not to be taken lightly, as it can have serious potential if it hits super effectively against threats such as Mewtwo. dealing upwards of 52.5% HP. And that's not even a critical hit!
Lastly, we have Swagger. This move is rarely used and it's usually filler, but it can prove useful if you
know your opponent is going to set up or if you're pitted against a Wall in an attempt to disrupt them. Or if you otherwise have a reason to use it over Sucker Punch.*
Other Options:
Hyper Cutter is only used to keep other Pokemon from weakening Mawile's Sucker Punch. Intimidate is undesirable as it will have the effect of indirectly weakening your Metal Burst. Sheer Force is also undesirable as it does not benefit Sucker Punch and therefore is only useful in the low tiers where you will want to run a different moveset anyway.
Super Fang is a good alternative for very bulky types, and it may actually prove better than Swagger. Allowing you to take out a large chunk of their HP if nothing else. Pain Split is listed as it serves a similar purpose to Super Fang, but until it becomes available, I can't be certain how reliable it will be. but I've listed it just in case.
Checks and counters:
Mawile is blessed with immunity to Toxic Spikes, Poisons (The usual methods, anyway), and Sandstorm damage. And as Taunt does not stop Metal Burst, you cannot count on it keeping you safe.
Unfortunately, until the day comes where Game Freak blesses Mawile with Sturdy, Mawile is checked by Spikes, Stealth Rock, Hail, Confusion, Sleep, Leech Seed, and Burns. As well as any pokemon that happen to pack a move that has low base power that will hit mawile for not very effective damage. In addition, Multi-hit moves are extremely effective counter against Mawile as well. Lastly, Mawile has an extremely low speed. But if you are able to send out a slower Pokemon or force Mawile to move faster than your own a la Trick Room or otherwise, it will be rendered crippled as Metal Burst does not have negative priority to prevent this.
Additional Comments:
In the event that Mawile
does someday gain Sturdy, I would suggest running it and Leftovers instead, allowing you to completely recover those hazards off with a single Protect. This would also open up the option of possibly abusing Wish/Healing Wish support.
*A rare example I've experienced was an online match I had. We were down to our last Pokemon: My Mawile was already expended at 1HP, and on the other side of the field was a full-health Volcarona. Sucker Punch was obviously not going to win me the battle. So I went for broke and used Swagger and landed it as their attack missed. Then I managed to stall them for the rest of the fight alternating between Protect, Sucker Punch, and Swagger. And won.
Of course, by no means am I saying that I wasn't just ridiculously lucky... But it can prove to be a good last resort option on occasion.