Sirfetch'd @leek
Ability: Scrappy
Nature: Adamant
EVs: 4 HP / 252 Atk / 252 Speed
-Meteor Assault
-Close Combat
-Leaf Blade
-Swords Dance
Honestly, not too complicated. Sirfetch'd isn't known to be great, but I love this thing when I want to troll my friends or something.
Scrappy, because duh, and leek to get a 50% critical hit in case getting a one-shot (which you probably will want, because the whole point is to surprise those friends that underestimate based on size) is a bit sketchy.
Meteor Assault has an amazing base power of 150, an accuracy of 100, and though it only has a max PP of eight, let's be honest-you don't need a lot of PP on moves for something you'll rarely want to use. Plus, the fact that it's a recharge move doesn't matter all too much, because the attack itself can often one-shot, and you still have 2 other quite viable attack options if you don't want to use it.
Close Combat is STAB, and it has base power of 120, so it's an easy choice.
Leaf Blade is a really good grass-type move, maybe not for coverage, but you might want to use it if you're up against a water-type and you want to just have something for that.
Swords Dance may not seem like a good choice, since Sirfetch'd's HP and defences aren't exactly sky-high, but if you're up against that-one-friend that decides to spam substitute and protect and roost etc on some tank with like no attack, then this is a good way to break that wall to add some attack, which will eventually make them run out of PP so you can land a one-shot blow with close-combat.
Even just if you realize that you can survive a few hits and that the game might last a while, you can also get an attack boost in.