Battle Spot: Octillery Trick Room and Doubles strategy

Build set as of Gen 6

Ability – Sniper 
Stats – HP (252), Special Attack/SpA (252), Special Defence/SpD (4)

Nature – Quiet
Item – Focus Sash

Moveset – Hydro Pump (stab), Fire Blast, Ice Beam, Protect

Similarly to Seviper's case, Octillery also suffers the same problem with average HP, defensive capabilities and horrendous Speed. On the other hand, its Attack and SpA stats are quite good, making it ideal for a Trick Room candidate wrecking destruction with a wide array of moves. Let's take a look of how the octopus should be used. 

Strength

As mentioned earlier, both Attack and SpA stat are high enough to cause damage to your opponent, that also makes your movepool vast and you have many options to choose from there. Staying true to its name, Octillery's role is just simply an artillery in your Trick Room and use it to your heart's content when the move is activated. Pretty straight forward here. 

If you're brave enough, you could let loose Protect and slot in another attacking move then give it Assault Vest boosting its SpD. As a pure Water-type, its two weakness Electric and Grass (not forgetting the rare Freeze Dry Ice-move) are usually SpA-based so that makes it tougher to take it down.

Weakness

Aside from the obvious poor defensive capabilities, Octillery’s abilities are somewhat less desired. It has Sniper, Sticky Feet and Moody. Sticky Feet is the most useless one and Moody is too random. So it’s better off with Sniper since critical hits in the current metagame seems to be appearing more now for some reason.

Also, since you're better off with all SpA-based moveset. That pretty much means the Attack stat is rendered useless, quite a pity to be honest, unless if you really want Gunk Shot then it's only recommended to max both Attack and SpA. Speaking of moves...

Moveset

Hydro Pump should be Octillery's main STAB move for good reasons, but Surf can do too if you have a Pokemon that benefits from it like Maractus. Your second move should be Fire Blast to get rid of those pesky Grass-type Pokemon, and Ice Beam as well for wide coverage.

If you already have a Pokemon that has a Fire or Ice move, Octillery still has plenty of moves left. Namely Gunk Shot, Seed Bomb, Scald, Energy Ball, Sludge Bomb, Flamethrower, Psychic, Waterfall and Flash Cannon. So many choices!

One interesting thing to note is it can learn Focus Power too, and if it wears a Scope Lens item it can easily OHKO most Pokemon 99% of the time with critical hit since it's compatible with Sniper ability. But in order for that to work, Trick Room is not the right choice and you'd need a Fake Out Pokemon for Octillery to setup, that would also mean you'd have to sacrifice Focus Sash and make way for Scope Lens, just be wary of offensive physical attackers. 

Closing thoughts

(image credit to _Absol_'s Bucket)

Generally, it’s a much better idea to go with the SpA build as it can learn a wide variety of TMs (and SpA TMs have higher power). If you want to go for a physical set, that's ok too but it will lack the artillery power compared to SpA. Had some fun with Octillery, but in the end, there are better Trick Room Water-type Pokemon out there such as Clawitzer and others. 

So Octillery, I choose you! Glhf!