Welcome, Pokemonsters, to one entry of The Type Tourneys blog series. This series is a theoretical series based on the idea of an in-game Friendly Competition where only Pokemon of one given type can compete. Each entry in the series will detail a general overview of the type and my predictions for what the main competitors and top tier threats in the tier. You guys can then discuss with me and tell me if you think I'm right, wrong or missed something crucial. More information on the series can be found at this link. The general rules for each tournament would be as follows:
 

• Double Battles Format; Bring 6, Use 4
• All Pokemon allowed; Includes Legendary and Mythical Pokemon
• All Moves, Abilities and Items are allowed; Includes Type-Changing Moves and Abilities
• Duplicate Pokemon and Items are allowed. (Due to restrictions, as we probably won't be able to officially ban them)
• No Smogon Clauses; i.e. Sleep Clause, Recovery Clause, OHKO Clause, etc.
• Pokemon with type-varying Forms may only participate in the correct Type Tourney; i.e. Alolan Vulpix only in Ice and Arceus-Ghost only in Ghost, etc.
• Mega-Form Pokemon are regulated by their base form; i.e. Mega Gyarados (Mega: Water/Dark, Base: Water/Flying) is allowed in Water and Flying, but NOT in Dark, etc.

Average Stats: 66 HP, 91 Atk, 107 Def, 60 SpA, 74 SpD, 51 Spe
Weaknesses: 
Resistances: 

Without further ado, let's begin the discussion on the Rock-Type in itself. As seen above, the Rock-Type is essentially a very ugly physically-based type. Therefore, Special moves could be more prevalent than in the other type tourneys; but only from good users of special attacks. It's also important to note that Sandstorm - and by association Sand Stream - will boost the special defense of all Rock-Types by 50%. The speed stat is also very low, meaning that fast mons will generally have an advantage - except in certain Trick Room situations. Finally, we see which attack types could be run extensively in this tournament. It's also important to note that Rock-type attacks are neutral on Rock-Type Pokemon; so the STAB boost could come in handy, in certain cases. Let's look at some of the picks for major threats: 

Arceus (Rock)

While allowing Legendary and Mythical Pokemon may end up being controversial, it's only fair to have a proper type showdown with them all included. And unsurprisingly, Arceus is possibly one of the major players. The first reason is that it has the highest BST of all Rock-Types, sitting at a 720 base total. Arceus is also extremely unpredictable because its movepool is so chock-full of coverage moves; it gets moves for each of the types that Rock is weak to; Surf/Aqua Tail/Waterfall (Water), Energy Ball/Giga Drain/Bullet Seed (Grass), Earthquake/Earth Power (Ground), Brick Break/Focus Blast (Fighting) and Iron Head / Flash Cannon (Steel). It also gets set-up potential with Swords Dance, Cosmic Power or Calm Mind, the ability to burn opposing threats with Will-O-Wisp, the potential to ruin Sand-users with Sunny Day or Rain Dance. In addition, it gets various methods of speed control - a very important ability in doubles - with Tailwind, Trick Room and Bulldoze or Icy Wind. It's one drawback is that Arceus can only run one of two items; Stone Plate or Rockium-Z. Rockium-Z will not affect Judgement's type but it does get Stone Edge and Rock Slide if it wants a STAB move. This does make it predictable and lowers the potential for using Z-Moves of other types, or running various berries,  leftovers or choice items, but even still, Arceus looks to be one of the most threatening Pokemon here; for sure. 

Diancie

Another mythical Pokemon that could be extremely scary. Diancie has absolutely insane bulk; with 150 Defense and Special Defense. However it is outclassed by a few other Pokemon in the highest Defense stat category, and outclassed by Shuckle for Special Defense. Then, you look at Diancie's attacking capabilities with both Special and Physical hits having a base 100 stat. Now, type-wise, she's not brilliant for offensive-types. The only real super-effective type she gets is Ground - with Earth Power. Earth Power will not hit the Rock and Flying dual-type Pokemon in this Tournament, but Rock-type moves such as Power Gem and Diamond Storm will hit them super-effectively. In addition, Diancie gets STAB Moonblast; something which can be used to hit threats like Tyranitar and Terrakion for extreme damage. Other options include Dual Screens, Calm Mind, Heal Bell and oh yeah... Trick Room. Diancie has a speed stat of 50 which makes her the joint-slowest user of Trick Room. Oh and by the way, Mega Diancie, if you want her, has the highest base Special Attack (by a good 33 points) of all Rock-Type Pokemon. Who needs coverage after all?

Terrakion

Close Combat, hi. That's basically it. Terrakion has an insane 129 base attack and a very fast 108 speed. With Close Combat hitting the majority of the tournament for high power super-effective damage, Earthquake and Iron Head hitting the rest, and then comes the options of a Rock-STAB move, Protect, Substitute, Swords Dance or even Taunt. While some Pokemon like Mega Diancie outspeed Terrakion, a scarfed Terrakion will always outspeed Diancie and has a 4x effective move in Iron Head. It's also important to remember that in Doubles, Justified can be very scary particularly with the new Dark-type move; Brutal Swing, to boost Terrakion's power. In general, Terrakion is a Pokemon that has one job, and does it well. But that's all it needs. 

Sand Stream

Sand Stream is an ability that creates an auto-sandstorm for five turns whenever the Pokemon who holds it enters battle. Sandstorm is known to chip away health from Pokemon that aren't Rock, Ground or Steel-type. The problem here is that every single Pokemon is Rock-type; so why use it? Because Sand also boosts the SpDef stat of Rock-Types by 50%. This could be used in combination with physical hitters to allow you to hit your opponent hard with physical hits, while they struggle to take your Pokemon out with Special moves. Tyranitar, in particular, is probably a better choice since it also has a Mega Form which has the second highest base-Atk of all Rock-Types (and only beaten by 1 point). It also gets Dragon Dance; a move that can be scary if left unchecked. However, if the 4x weakness to any Fighting-type move puts you off, then Gigalith is a nice alternative. 

Flying-Types

This is probably a shocking option because Rock/Flying types are automatically weak to STAB Rock moves making them a huge target. However, not all Pokemon tend to run Rock moves if they think they can get away with coverage moves only. Also, a lot of Rock-types may just carry Earthquake; a move that these are immune to. Aerodactyl is the fastest Rock-type Pokemon of all, and it's mega evolution has an even higher Speed-stat; and gains Tough Claws. It can also run Earthquake and Aqua Tail itself, and gains the move Sky Drop - which while Not Very Effective on Rock-Types - will negate opponent's moves if used correctly. Tailwind is also a nice option to set up speed in difficult situations for the rest of the team. Minior and Archeops can be useful too but Aerodactyl seems like the best pick here. 

Cradily

Perhaps a shocking pick here, because Cradily is not the strongest, nor the fastest, nor the slowest, nor the bulkiest. But, what Cradily does have going for it, is that it's the only Pokemon with a STAB Grass-type move in the Tournament. In addition, it also gets the Storm Drain ability which makes it immune to Water-type moves. Cradily gets STAB on the likes of Giga Drain, Energy Ball or Seed Bomb, as well as getting a Water-type move in Brine and both Earth Power and Earthquake for coverage. It can also set up major defenses with the likes of Barrier or Amnesia, can sit behind a Substitute, can Toxic foes and stall them with Synthesis or Recover, and it can even pull out Mirror Coat if your opponent tries to hit it with special moves. It's the one to watch here, honestly. 

Aggron

I can hear you all gasping and serving severe confusion after this choice. You'll be immediately trying to clock me with the possiblity of a 4x hit from Ground or Fighting types. While, yes, that's true, it's also not. Aggron has a Mega Evolution; and when it mega evolves, it loses its rock-type. This makes it pure Steel-type and it has the ability Filter, which reduces damage to 3/4 by super effective hits. Not to mention, it ties Shuckle for the highest Defense stat in the tier and carries STAB Heavy Slam or Iron Head off an insane 140 base attack. While specially, it's not outstanding, it can certainly be clutch if there's mainly physical hitters on opposing teams. 

Water-Types

Water is super-effective on Rock... that's it. Having a STAB water-move is going to - likely - be more useful than having a non-STAB one. In addition, these guys also only take neutral damage from a Steel-type move. However, they do take 4x damage from Grass-type users, either in the form of Cradily, or others using non-STAB Grass-Type moves. Realistically, Omastar looks to be the best bet here, with the option of Shell Smash, and then a complete sweep with its massive Special Attack stat, combined with STAB from Hydro Pump and the likes of Ice Beam or Earth Power to hit Cradily hard. The others could find their uses too if more bulk, or more physical preference is needed. 

Sturdy

All of the above have the potential for one of the most annoying abilities in the entire game of Pokemon; Sturdy. I'm sure those of you who've played a game from Gen 5 onwards know exactly what I'm talking about. Before Gen 5, Sturdy only activated on OHKO moves like Horn Drill. But since then, Sturdy became the bane of everyone's existence by guaranteeing survival from the first hit - almost like a focus sash. Now, a lot of these Pokemon have major weaknesses that can be played around, but never underestimate the threat of a Sturdy Pokemon who could set up something with their turn to allow other teammates to shine through. 

Niche Picks

These two have been grouped together because they're going to tend to be niche picks. Rampardos has the highest base Attack of all Rock-type Pokemon and also carries the insane Sheer Force ability. Pairing this with a Life Orb allows Rampardos to increase his damage output by 1.69x without taking recoil - from moves that have added effects; such as Iron Head. However, it is a slow Pokemon, and even with a scarf, will not outspeed the fastest threats. Unfortunately a lot of Rock-types are slower than it and it maybe can't do the job either in Trick Room. Whereas Nihilego is a decently fast Pokemon with the second highest base Special Attack of all Rock-types (second to Mega Diancie). The main draw here would be the use of Beast Boost, the move Grass Knot to hit most Rock-types, and then Thunderbolt to hit Fliers and Hidden Power Ground or Fighting for Steel-types; for lack of a better option. It also does get Brutal Swing to pair with Terrakion, and Toxic Spikes can be extremely annoying to deal with. However, Nihilego is frail defensively and is 4x weak to the likes of Earth Power and Earthquake. Both of these can work with support, or can support teammates, but aren't the absolute top tier here. 

So, tell me what you think? Am I spot on, did I miss something, do you disagree? What team would you think about running in a Rock-type Tourney; if we ever got the feature updated in a future game. Let me know down below bbs. Next up is the Water-type; see ya then!