XY/ORAS Singles Showdown Overused Team advice

[Luckii]

Rightio, I've created a new OU team on Pokemon showdown, and I think it needs a bit of work. The core of the team is good, but I'm struggling to find a final Pokemon to slot in.

Conkeldurr (M) @ Life Orb
Ability: Guts
EVs: 252 Atk / 4 SpD / 252 HP
Adamant Nature
- Drain Punch
- Ice Punch
- Bulk Up
- Mach Punch

Heatran (M) @ Choice Scarf
Ability: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Flamethrower
- Flash Cannon
- Earth Power
- Ancient Power

Venusaur-Mega (M) @ Venusaurite
Ability: Thick Fat
EVs: 252 HP / 240 Def / 16 Spe
Bold Nature
- Giga Drain
- Sludge Bomb
- Synthesis
- Sleep Powder

Greninja (M) @ Life Orb
Ability: Protean
EVs: 4 Atk / 252 SpA / 252 Spe
Hasty Nature
- Hydro Pump
- Dark Pulse
- Ice Beam
- U-turn

Skarmory (F) @ Leftovers
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Roost
- Brave Bird
- Stealth Rock
- Defog

Last Slot: ???

Initially I has Choice Specs Latios in the final slot, but then soon discovered my team's weakness to opposing Latios once Greninja has been taken care of. I've also tried regular Gengar, but then my team was horrifically weak to Psychic types. I'm a little stumped. Would any of you mind giving me a hand? Obviously improvements to the other Pokemon are welcome!

 

[KoL]

Right off the bat I can tell you that Latios absolutely hates Tyranitar and Aegislash, the former due to the Sp.Def boost it gets from sandstorm, the latter due to Shadow Sneak and resisting both of Latios's STAB moves and both of them can learn Pursuit, allowing them to effectively trap Latios on the field and kill him with ease. If you want a means to handle Latios, I'd go for either of them, although note that Aegislash hates being Tricked Choice items if you go that route.

As for the team:

- You might as well run Flame Orb on Conkeldurr if you're going to use Life Orb and Guts since if you're afraid of burns, Guts won't help you live through Life Orb and the burn (that I presume you plan to switch into) both draining your HP, and Drain Punch won't be able to keep up with that damage if your opponent switches in things that resist it. Using Iron Fist could be an option here since in all likelihood players will avoid burning Conkeldurr out of fear of Guts anyway.

- AncientPower is dreadful and Fire Blast is superior to Flamethrower on Heatran overall - the extra damage matters more than you'd think. Drop AncientPower for Dragon Pulse if anything.

- Synthesis isn't too great a move due to Tyranitar's prevalence ruining it, although if an opponent runs Zard Y you can get boosted heals. I'd run Leech Seed over Synthesis myself due to how good it forces switches, and allows Venusaur to passively regain HP as it does its work.

- Consider Grass Knot on Greninja to give yourself a type that resists Electric and Grass. Other than that you can't really go wrong with a Greninja set like that.

- If Skarmory runs Defog I'd honestly have Heatran use Stealth Rock since Skarmory really likes Whirlwind, and you currently lack a PHazing 'Mon.

There's not much to say beyond that except that your team is a bit overloaded with attacks. With no setup moves, status moves etc. you may find yourself being brickwalled by certain defense cores.