find me a last Pokemon for competing in VGC?

I have most of the team worked out, I just need a sixth, this has been giving me trouble for about a week now and everything I try just fails epically. also please bring to my attention any major weaknesses you can identify thank you.

Octillery, Medicham, Swalot, Jolteon, Forretress, ???

Lead with

Octillery

Nature: Modest

Ability: Sniper

Item: Expert belt

Evs: Def 128, Sp-Atk 252, Sp-Def 128

Moves: Flamethrower, Ice beam, Surf, Energy ball/ Charge beam

Octillery with this moveset can OHKO nearly any other lead or at least hit them for double damage, even if they survive the first hit with focus sash or something his Def and Sp-Def can withstand most non-super effective attacks.

Medicham

Nature: Jolly

Ability: Pure power

Item: Life orb

Evs: Hp 4, Atk 252, Spe 252

Moves: Brick break, Thunderpunch, Ice punch, Psycho cut

Brick break to counter Tyranitar, Thunderpunch and Ice punch to add to my teams coverage as I don't want to have to rely on Octillery to take out Dragons on his own, Psycho cut to take out Machamp and other pesky Fighting and Poison types. life orb is optional as it can easily be replaced by leftovers but I prefer an almost guaranteed OHKO on most Pokemon to longevity on Medicham.

Swalot

Nature: Adamant

Ability: Liquid ooze

Item: Black sludge

Evs: Hp 252, Spe 128, Sp-Def 128

Moves: Gunk shot, Fire Punch, Rest, Sleep talk

Basic Restalk tactics with physical attacks not much else to say really.

Jolteon

Nature: Hasty

Ability: Volt absorb

Item: Magnet

Evs: Hp 4, Spe 252, Sp-Atk 252

Moves: Baton pass, Thunderbolt, Magnet rise, Charge beam/Shadow ball

Super speed Joteon with magnet rise is hilarious when switching in on a Camerupt using Magnet rise then baton pass to change to Octillery and surf it to death Charge beam could also be used to raise Octillery's Sp-Atk then Make them Hurt even more. Alternatively use Shadow ball or Thunderbolt to do fair damage without switching.

Forretress

Nature: Relaxed

Ability: Sturdy

Item: Leftovers

Evs: Hp 252, Def 128, Sp-Def 128

Moves: Gyro ball, Toxic, Giga drain/Rest, Explosion

It takes a long time to wear Forretress down and by that time one maybe two Pokemon have been Toxiced and Gyro balled to death. To increase longevity use rest or Giga drain or to take out an impossible foe e.g Salamence or Infernape use explosion to take a massive chunk out of their Hp in Preparation for a quick demise by Medicham or Octillery.

???

Nature: ???

Ability: ???

Item: ???

Evs: ???

Moves: ???

Needs to be filed with either a fire or dark I tried Houndoom and it didn't work so please don't suggest him unless you have an original set. A Grass type might also work well but I have also tried Cacturne and Shiftry and came to despise them but same as with Houndoom if you have a new set tell me and I will try it out completely un-biased.