Trying to make a Mono-Ghost Team, but I'm kind of newbie at this.

So far I've got:

Sableye @ Lum Berry
Ability: Prankster
EVs: 248 HP / 188 Def / 72 SDef
Bold Nature
- Taunt
- Will-O-Wisp
- Recover
- Foul Play

Aegislash @ Spooky Plate
Ability: Stance Change
EVs: 252 HP / 252 SAtk / 4 Atk
Quiet Nature
- King's Shield
- Shadow Ball
- Sacred Sword
- Shadow Sneak

Chandelure @ Choice Specs
Ability: Flash Fire
EVs: 252 Spd / 252 SAtk / 4 Def
Modest Nature
- Fire Blast
- Shadow Ball
- Energy Ball
- Dark Pulse

Gengar @ Gengarite
Ability: Levitate
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature
- Shadow Ball
- Perish Song
- Disable
- Destiny Bond

Trevenant @ Leftovers
Ability: Natural Cure
EVs: 252 HP / 180 Def / 76 Spd
Impish Nature
- Horn Leech
- Rock Slide
- Will-O-Wisp
- Rest

All sugestions for the 6 slot would be much apreciated, also it would be great to hear suggestions for changes or weaknesses that i should cover