Shadow Force (Power: 150)
shadow ball is the strongest ghost TM
I don't know about Pokemon black and white, but in Generation IV the strongest ghost move is Shadow Force, but only Giratina can learn it. A decent ghost move is Shadow Ball if you can't get an Action Replay DS.
Shadow Force
The Strongest flying move in Pokemon Sapphire is 'Sky Attack'5PP140 Attack90 Accuracy
the strongest move is growl ill think you'll find that the strongest move is splash
Fissure
Morty has ghost-type Pokemon, it's best to use a Pokemon that know's a dark type attack. Ghost Pokemon do not have many weaknesses but dark is strongest against them.
The move is Doom Desire
hydro cannon
Depends what move it has
A ghost type move.
The strongest is Focus Punch with 150 power, but is not a good move unless you are behind a Substitute.