Levitate and Pressure are already Waaaaay too OU for a Ghost.
Guts is too used for a fighter.
Vital Spirit might work.
Hmmm, didn't think it would be this tough.
Ghost type abilities:
Pressure
Levitate
Insomnia
Wonder Guard
Keen Eye
Stall
Snow Cloak
Aftermath
Unburden
We can pretty much axe this entire list, bar Insomnia, Keen Eye, and Stall.
Fighting type abilites:
Anger Point
Vital Spirit
Damp
Water Absorb
Guts
No Guard
Reckless
Limber
Keen Eye
Iron Fist
Swarm
Steadfast
Intimidate
Technician
Blaze
Effect Spore
Poison Heal
Thick Fat
Pure Power
Inner Focus
Anticipate
Dry Skin
Since I doubt this will be getting Damp, Water Absorb, No Guard, Limber, Iron Fist, Blaze, Effect Spore, Poison Heal, Swarm, Thick Fat, or Dry Skin through any kind of logic, that leaves a few options.
Some would be overpowering. Pure Power and Technician fall in this category.
Guts and Intimidate are so prevalent it isn't even funny.
This leaves, with the Ghost list:
Insomnia
Keen Eye
Stall
Anger Point
Vital Spirit
Reckless
Steadfast
Inner Focus
Anticipate
I suppose you could argue about the power of Anger Point on something so bulky, but if FSS stays on top it only has uh, 65 Base speed. Even Rhykune's 7- doesn't make a +6 Attack after CH, even with a miraculous Salac Berry an unbeatable threat. Although if it has Shadow Sneak or Mach Punch it could be... troublesome.
Reckless only helps it if we give it HJK. Steadfast is an interesting option, although flinch moves aren't prevalent, and even though it could theoretically make Togekiss cry if it worked, it won't. The rest are mostly throwaway abilities, and Insomnia and Vital Spirit are clones.
Other possible choices could be Own Tempo and Synchronize.
	
		
	
	
		
		
			hmmm an ability thats not typical for a ghost ie not pressure/insomnia/or levatate...SIMPLE. give it simple. simple and steadfast.
		
		
	 
We're gonna give a pokemon basically begging to use Bulk Up the Simple ability? No way matey. +2 Atk and Def in one move? Not to my liking.