So here is my team. I need help deciding the last slot.

Mawile @ Mawilite
Adamant
Intimidate
~Play Rough
~Iron Head
~Sucker Punch
~Swords Dance
252 Atk 252 Spe 4 HP

Houndoom @ Sitrus Berry
Timid
Flash Fire
~Nasty Plot
~Fire Blast
~Dark Pulse
~Sludge Bomb
252 SpAtk 252 Spe 4 HP

Toxicroak @ Black Sludge
Adamant
Dry Skin
~Bulk Up
~Poison Jab
~Brick Break
~Stone Edge
244 HP 132 Atk 132 Def

Volcarona @ Life Orb
Modest
Flame Body
~Quiver Dance
~Bug Buzz
~Firey Dance
~Giga Drain
252 Spe 252 SpAtk 4 SpD

Rotom-W @ Leftovers
Clam
Levitate
Volt Switch
Hydro Pump
Thunder Wave
Paint Split
252 Hp 252 SpD 4 SpAtk

I'm having a hard time deciding on my 6th pokemon.

I feel like I need a good wall or maybe some spiker. What do you all think?