Help me pick a 6th Pokemon for my team?

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I've finally found success on Battle Spot with this team, but I'm having trouble with picking a 6th Pokemon. For now I've been switching back and forth between (Hyper Voice) Sylveon and Heat Rotom (listed here), but Sylveon is super predictable these days and people have ways to counter it. I was thinking of adding Heatran (I like it's moveset/typing) or Terrakion but I'm not sure. Let me know what you think of my team!

Crystal (Suicune) @ Leftovers

Ability: Pressure
Level: 50
EVs: 232 HP / 84 Def / 112 SpA / 80 SpD
Calm Nature
IVs: 0 Atk
- Tailwind
- Scald
- Ice Beam
- Protect

I. LOVE. TAILWIND. Also having Ice Beam to deal with Dragons & Scald to dish out decent damage/burns isn't too bad either. I usually lead with Suicune to set up Tailwind. I really like how Suicune works well with Gengar/Venusaur. My only complaint with Suicune is that trying to get decent IVs/Nature in game is so obnoxious.

Gengar (M) @ Focus Sash
Ability: Levitate
Level: 50
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Sludge Bomb
- Taunt
- Will-O-Wisp
- Shadow Ball

Gengar is pretty cool. Started using it after I saw one of Cybertron's vids recently. (I've been trying to get back into VGC, so you see my team is super similar hahah. Hopefully once I get back into it, I'll think of some new stuff.) I like his ability to dish out damage (or burns) super fast to start off. I like leading with him, or keeping him in the back to switch in later on an ineffective move. I haven't been using Taunt much (besides when you see the obvious), but it's still pretty nice. I considered recently making him bulkier and changing his item to screw with people (because I'm sure people will catch on with this set) but for now I'll leave it how it is.

Bisharp (M) @ Life Orb
Ability: Defiant
Level: 50
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Knock Off
- Sucker Punch
- Iron Head
- Protect

Pretty self-explanatory. Bisharp wants to kill everything. Defiant is awesome. He's become one of my favorite Pokemon recently. That's all.

Salamence (F) @ Salamencite
Ability: Intimidate
Level: 50
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Double-Edge
- Fire Blast
- Roost
- Protect

I originally was using Special Salamence but I've had WAY more success with the physical build. Double-Edge is awesome, and you have roost to gain back HP if you need it. Fire Blast is also handy to have too. 

Venusaur (M) @ Venusaurite
Ability: Chlorophyll
Level: 50
Shiny: Yes
EVs: 252 HP / 240 Def / 16 Spe
Modest Nature
IVs: 0 Atk
- Giga Drain
- Sludge Bomb
- Leech Seed
- Protect

Venusaur is a new addition to my team too, I forgot how much I loved M-Venu. He can basically take any attack and still be able to dish out damage too. I like having Leech Seed to slowly leech (lol) away at my opponents while gaining HP back at the same time. (I originally had Synthesis on him instead. Also Modest nature because that's what my one on my game is, originally I had more EVs invested in Sp Atk. Just saying. Not tryna to breed another 5IV Venu lol.) I also love now that I have Venu, I have a choice with my Mega. Just having Salamence was SUPER obnoxious because it was so predictable. 

Pizza Rollz (Rotom-Heat) @ Sitrus Berry
Ability: Levitate
Level: 50
EVs: 252 HP / 4 SpA / 252 SpD
Calm Nature
- Electroweb
- Thunderbolt
- Will-O-Wisp
- Overheat

Ahh good 'ol Rotom. I chose Rotom Heat because I desperately needed a Fire type on my team. I did have Rotom Wash at one point but changed my mind. This is the usual build I use for Heat or Wash Rotom, besides one move. I changed Protect to Electroweb. Electroweb is a lot of fun, it lowers the opponents speed by one stage and damages them a little bit. Rotom Heat is a pretty solid choice, except Landorus/anything with Rock Slide scares me a LOT. Should I invest more Def EVs in? Or keep him how he is? I'm considering changing out Rotom for a better Fire type (Heatran maybe?) or keeping him for now. Let me know what you guys think!