The 5 best Pokemon you aren't using (Smogon Doubles)

Running 6 standard Pokemon with 6 standard movesets can only get you so far. Sure you have a solid team, great synergy, and there is a reason that movesets and threats are standard (hint: because they work) but you also become very predictable. The difference between a good team and a great team is that great teams juggle standard threats/movesets with creativity, and are able to get an advantage over the opponent before the battle even begins.
Here are my 5 favourite not-so-often-seen Pokemon to use in Smogon Doubles, my favourite set, notable moves, and why they aren't often seen.

Landorus	Ground/Flying Type	89 HP / 125 Attack / 90 Defense / 115 SpAtk / 80 SpDef / 101 Spd
Abilities:	Sand Force (This Pokemon's Rock/Ground/Steel attacks do 1.3x in Sandstorm; immunity to it)
		Sheer Force (This Pokemon's attacks with secondary effects do 1.3x damage; nullifies the effects)
Notable Moves:	Earth Power, Focus Blast, Psychic, Sludge Bomb, Sludge Wave, Brick Break, Earthquake, Iron Tail, Rock Slide, Stone Edge, Superpower, U-Turn

twitch.tv/kylecol3 (Landorus) @ Life Orb
Ability: Sheer Force
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature
- Hidden Power [Ice]
- Earth Power
- Psychic
- Protect

Landorus I is a beast. After the Sheer Force boost, the Life Orb Boost, and STAB, Earth Power is almost as strong as a Mega Kangaskhan Return. I love to run this set beside Mega Kangaskhan to beat opposing Landorus-T, Hitmontop, Aegislash, and Scrafty that aren't carrying Ice Punch. Landorus I isn't seen very often in doubles because as powerful as it it, Landorus-T has far more viability and diversity in it's movesets, and you can only run one of the two. A physical set is also possible as Landorus has a higher base physical attack, but most of its physical movepool is not affected by Sheer Force, so running a physical set on a sand team with Sand Force would be interesting and usable.

Moltres		Fire/Flying Type	90 HP / 100 Attack / 90 Defense / 125 SpAtk / 85 SpDef / 90 Spd
Abilities	Pressure (If this Pokemon is the target of a foe's move, that move loses one additional PP)
Notable Moves:	Air Slash, Extrasensory, Fire Blast, Heat Wave, Hurricane, Morning Sun, Overheat, Roost, Tailwind, Sunny Day, Will-O-Wisp, Ancient Power,  Sky Drop

I never miss (Moltres) @ Sitrus Berry
Ability: Pressure
EVs: 252 HP / 252 SAtk / 4 Sdef
Modest Nature
- Heat Wave
- Tailwind
- Hurricane
- Protect

Moltres is outclassed as a special attacker by Mega Charizard Y, and a Tailwind setter by Talonflame, so the only way to make Moltres stand out is to combine the 2. Moltres has decent bulk, and when invested can be counted on to take a hit before setting up Tailwind. Moltres is pretty uncommon due to its very specific niche, and because it is 4x weak to the common Rock Slide. Moltres is a very powerful Pokemon in its own right however and with decent stats all around, Moltres can certainly pull its weight on the right team.

Mega Charizard X	Fire / Dragon Type	78 HP / 130 Atk / 111 Def / 130 Spa / 85 SpDef / 100 Spd
Abilities:	Tough Claws (This Pokemon's contact attacks do 33% more damage.)
Notable Moves:	Belly Drum, Body Slam, Dragon Claw, Dragon Dance, Dragon Rush, Dragon Tail, Earthquake, Flame Charge, Flare Blitz, Outrage, Iron Tail,  Rock Slide, Thunder Punch, Will-O-Wisp

Charti Kale (Charizard) @ Charizardite X
Ability: Blaze
EVs: 252 HP / 252 Atk / 4 SDef
Adamant Nature
- Flare Blitz
- Dragon Claw
- Protect
- Dragon Dance

After 1 dragon dance adamant Char X outspeeds Jolly Mega Kangaskhan, Jolly Terrakion, and speed invested Landorus T, and can OHKO all of them. (100% to OHKO kanga at +1 with flare blitz, 75% to OHKO Terrakion with Dragon claw at +1, and 87.5% to OHKO speed invested Lando T with Flare Blitz at +0). 252 HP also guarantees you will live a Return from Adamant Mega Kangaskhan and Stone Edge from Jolly Terrakion (if mega obviously) so you should have no problem setting up a DD and sweeping. If you manage to get up a second Dragon Dance you can OHKO standard Cress (252 HP / 60 def / +196 SDef) so you pretty much win the game.
An alternative Spread of 128 HP / 252 Atk / 128 Spd can be used if you want to outspeed Deoxys A and Mega Aero after 1 boost but I rarely see either of these 2 and Deo is always carrying a sash anyway so I like to stay nice and bulky.
This set performs best as a late game sweeper in my experience, so make sure you bring teammates than can eliminate threats like Scarf landorus, Follow me Togekiss, SS Kingdra etc. Ferrothorn is a great partner to deal with these mons.

One last thing, If you want to replace one of these attacks with Earthquake to beat Heatran you can, but Earthquake only has a 25% chance to OHKO before one Dragon Drance and you miss out on a lot of KOs if you give up one of the other moves. If you want to run jolly with 3 attacks then EQ never OHKOs tran so it isnt worth it imo.

The reason that no one uses Charizard X is because Mega Charizard Y is just so powerful, and has access to spread and can bring the sun with its ability Drought. But if you need a powerful quad resist to fire, you want to sweep almost the entire meta with one boost, and you have an empty mega slot, Charizard X is the Pokemon for you.

Musharna	Psychic Type	116 HP / 55 Atk / 85 Def / 107 SpAtk / 85 SpDef / 29 Spd
Abilities	Forewarn (On switch-in, this Pokemon is alerted to the foes' move with the highest Base Power)
		Synchronize (If another Pokemon burns/poisons/paralyzes this Pokemon, it also gets that status)
		Telepathy (This Pokemon does not take damage from its allies' attacks)
Notable Moves:	Baton Pass, Calm Mind, Charge Beam, Dazzling Gleam, Energy Ball, Healing Wish, Hypnosis, Moonlight, Pain Split, Psychic,  Psyshock, Shadow Ball, Signal Beam, Stored Power, Thunder Wave, Trick Room, Helping Hand, Skill Swap

Pillow Kale (Musharna) @ Sitrus Berry
Ability: Telepathy
EVs: 128 Sdef / 252 HP / 128 Def
Relaxed Nature
- Baton Pass
- Helping Hand
- Psyshock
- Thunder Wave

With such great Utility and Bulk, as well as access to a fantasic ability in Telepathy why isn't Musharna seen more often? Well its outclassed in almost every aspect by Cresselia, who is bulkier, has a better movepool, and avoides friendly Earthquake thanks to Levitate. Musharna does have a unique niche in that it is a slow Baton Pass user. While many people assume that Baton pass is only for passing off boosts from Geomancy or Shell Smash Smeargle, a slow Baton Pass guarantees a safe switch into some of your frail Pokemon like Deoxys A and Talonflame, who have trouble switching in but wreak havoc once they enter the battle.

The EV spread I have above makes Char Y's heatwave a guaranteed 3hko with the rest into physical bulk.

Virizion	Grass/Fighting Type	91 HP / 90 Atk / 72 Def / 90 SpAtk / 129 SpDef / 108 Spd
Abilities:	Justified (This Pokemon's Attack is boosted by 1 after it is damaged by a Dark-Type Attack)
Notable Moves:	Close Combat, Energy Ball, Focus Blast, Giga Drain, Leaf Blade, Sacred Sword, Stone Edge, Superpower, Swords, Dance, Synthesis, X-Scissor, Zen Headbutt, Helping Hand, Quick Guard,

deer kale (Virizion) @ Lum Berry
Ability: Justified
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature
- Stone Edge
- Close Combat
- Leaf Blade
- Protect

Virizion is one of the few Pokemon that can check Mega Kangaskhan, Rotom-W, and Mega Charizard Y in a single moveset. It outspeeds and can super effectively hit all 3, OHKOing Char Y and non HP invested Kangaskhan. The reason that Virizion isn't seen very often is that it has poor attacking stats, and while it can check these major threats, it isn't particulalry great at checking any one of them. If you find yourself looking for a 6th team member however, and you want extra insurance against some common threats, then Virizion is for you!