I wanted to make this post like two weeks ago but never got around to it.
Here's a few Pokemon I've used on and off that don't get a ton of attention when they're actually fantastic.
Mega Manectric
Mostly dismissed at the beginning of XY, Mega Manectric is actually pretty cool for outrunning the fastest common Pokemon in the metagame - Shaymin-S. As we've seen with Lando-T, Intimidate and a switching move is an excellent combination, and on top of that Manectric gets STAB on Volt Switch. Electric STAB is also pretty nice right now, hitting Charizard Y, Gyarados, Keldeo, and Togekiss for super effective damage and getting excellent neutral coverage (the most common Electrics don't resist Electric). A quick HP Ice disposes of stuff like Lando-T, Garchomp, and Shaymin-S. It even gets Overheat for the bulky Grass-types that normally wall it (although it's hard to justify giving up any of its typical moves). Just ensure you run enough Speed to outrun Garchomp before Mega Evolution and you cover basically everything relevant. I'm personally curious about a defensive set - I've used a Raikou set with TWave / Snarl / Volt Switch to Laga-smashing success and I wonder if Mega Manectric would accomplish it better or not.
Suicune
Suicune got a bit of discussion in the posts above mine but I might as well expand on it a bit. Its bulk really is fantastic and it gets some excellent moves to compliment it. I've been running an EV spread of 232 HP / 32 Def / 128 SAtk / 84 SDef / 32 Spd Bold on a team of mine and it's really neat what it can do, avoiding a 2HKO (with Sitrus) from all of Adamant Mega Kangaskhan's Return and 136 Modest Rotom-W's Thunderbolt in addition to avoiding the KO from Modest Shaymin-S's Seed Flare. Ice Beam with the SpA EVs OHKO's Shaymin-S and Lando-T. Snarl is great, lowering the opponent's SpA behind Substitutes (hello Heatran) while getting some decent chip damage in - and unlike the average Icy Wind user (hello Cress), it threatens Bisharp with a burn from Scald. We all know how Tailwind works too, and Suicune is an excellent Tailwind setter - it unfortunately shares the Electric weakness that most setters have, but it's neutral to Rock and doesn't give a fuck about Ice.
Flareon
this thing is legit stronger than Darmanitan after a Guts boost ;)
A few other Pokemon I've considered looking at some more:
- Tornadus - itemless Acrobatics still puts in work, and its Speed gives unreliable priority user Bisharp some competition (although its bulk is awful)
- Shaymin-S - fast, strong, destroys most Sleepers, and okay haxing things is fun
- Zapdos - Competition with Thundurus as far as typing goes, but Heat Wave and Tailwind let it stand out
- Gourgeist-Super - cool TR setter, bulky as fuck, dgaf about Spore