Please no Giratina, please no break monotype :[In reality, for ghost, the issue isn't viable attackers. Although Aegislash fills an excellent role as one of the few strong physical attackers in ghost, it is not the only one. Rather, Aegislash aggravates the typing's fire weakness (perpetuated by the type's reliance on Will-O-Wisp to compensate for its lack of consistent bulk), and offers unreliable bulk at best in Shield Form. It has one status move, in Toxic, but doesn't have access to Will-O or Thunder Wave itself to act as a supporting mon, so most ghost users are forced to rely on their 'bread and butter' in the form of Gourgeist, Jellicent, Doublade, Cofagrigus, or others. The thing about ghost, though, is that no one team is the same. There isn't a mold that can be accepted that makes the team strong enough, but its issue isn't a lack of a physical attacker (found in Banette, in Golurk, and in Trevenant, if needed, all offering the same level, or greater, of coverage for a ghost team) but rather in its lack of a reliable way to get rid of hazards.
Ghost has one Pokemon that is legal that has access to the move defog. No ghost type learns rapid spin. This Pokemon is Drifblim, and for the many people out there unfamiliar with Drifblim, its base stats are 150/80/44/90/54/80 (BST of 498). It has access to the abilities Aftermath, Unburden, and Flare Boost (1.5x special attack when burned). It's not viable as a serious attacker given these stats. Its special attack is barely able to overtake Gengar in power, but due to its speed, without investment, it will be outsped and killed by most variants of Bisharp. Assuming that Drifblim has switched in to Defog at any point in the game, it is at most at 75% health.
252+ Atk Bisharp Knock Off (97.5 BP) vs. 252 HP / 252+ Def Drifblim: 390-462 (77.3 - 91.6%) -- guaranteed OHKO after Stealth Rock
Being OHKOed by Bisharp is not a new thing for ghost type, but that's just a fact to life with the typing. Unfortunately, its best walls are Ubers material. Not many things can OHKO Drifblim, thankfully, but unlike some other Defoggers (Namely all of Flying type), Drifblim has no access to Roost or any recovery except for Pain Split (a highly unreliable recovery at that), so although it barely lives Flare Blitz from Charizard X (Not guaranteed)
252+ Atk Tough Claws Mega Charizard X Flare Blitz vs. 252 HP / 252+ Def Drifblim: 331-390 (65.6 - 77.3%) -- 25% chance to OHKO after Stealth Rock
252 Atk Reckless Staraptor Brave Bird vs. 252 HP / 252+ Def Drifblim: 256-303 (50.7 - 60.1%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Gyarados Ice Fang vs. 252 HP / 252+ Def Drifblim: 176-208 (34.9 - 41.2%) -- 64.5% chance to 2HKO after Stealth Rock
On the special side
252 SpA Alakazam Psyshock vs. 252 HP / 0 Def Drifblim: 255-301 (50.5 - 59.7%) -- guaranteed 2HKO after Stealth Rock
252+ SpA Hydreigon Dark Pulse vs. 252 HP / 252+ SpD Drifblim: 290-344 (57.5 - 68.2%) -- guaranteed 2HKO after Stealth Rock
252 SpA Mega Charizard Y Fire Blast vs. 252 HP / 252+ SpD Drifblim in Sun: 325-384 (64.4 - 76.1%) -- 12.5% chance to OHKO after Stealth Rock
There is no doubt that Drifblim has decent bulk and some uses, but it's not able to consistently pull through for a team. Unfortunately, it's not even on the roster of most teams because, outside of Defogging, it doesn't have real use. It tends to run a full support set (Baton Pass Sets, Will-O, Walling Sets) all paired with Defog in an attempt to make it viable, but it's few and far between.
Drifblim is not the only Pokemon that has access to Defog, though, as both of the other Ubers for Ghost Type, Arceus and Giratina, have access to Defog. Arceus has too strong of a movepool to be considered to be brought down, but Giratina has genuine potential for being brought down. Although it is a strong Pokemon, it is restricted in its own ways. It's considered one of the greatest walls in the meta, granted a strong typing in ghost/dragon, but it has limited coverage offensively (Running Dragon Pulse, Shadow Ball, Rest Talk and some other variants, but never really anything groundbreaking coverage wise) and is still walled effectively by some popular sets in the meta (especially Assault Vest sets, walled horrifically by special walls of all types) and is eventually forced to try and overpower by maxing boosts. It gets phased easily because of its reliance on Rest as recovery. This variant will be stopped mostly by physical attackers, and variants running Physical Bulk without Calm Mind, opting to burn, will be disposed of effectively by special attackers as well.
252+ Atk Bisharp Knock Off (97.5 BP) vs. 248 HP / 252+ Def Giratina: 216-254 (42.9 - 50.4%) -- 42.2% chance to 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Life Orb Mamoswine Icicle Crash vs. 248 HP / 252+ Def Giratina: 252-299 (50 - 59.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Mega Garchomp Outrage vs. 248 HP / 252+ Def Giratina: 306-360 (60.8 - 71.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Gengar Shadow Ball vs. 248 HP / 252+ SpD Giratina: 186-218 (36.9 - 43.3%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
252 SpA Latios Draco Meteor vs. 248 HP / 252+ SpD Giratina: 270-320 (53.6 - 63.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
232 SpA Pixilate Mega Gardevoir Hyper Voice vs. 248 HP / 252+ SpD Giratina: 288-342 (57.2 - 67.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
It is relatively effective at deflecting hits with its bulk, designed towards blocking these attacks, and the concern with bringing it down would be its Calm Mind set just for its ability to wall both Physical and Special Attackers effectively. At base 100 attacks, 120 in Origin Form, it's a decent attacker, but not a threat, another reason that people run its Calm Mind set.
TL;DR, Bring down Giratina, despite its holding in ubers, for ghost typing to bring an option for Defog and a more reliable wall for ghost typing (The type plagued by Pokemon that either have high defensive stats or a high HP stat, never both, never balanced.)
Nothing would be able to beat the Rest Talk CM set. Rest, Sleep Talk, Calm Mind, Dragon Pulse / Shadow Ball / Some Move. It doesn't matter if it resists if it's at +6 .3.
Also, it's Wil-o-wisp + Dragon Tail set would screw so many people over.
It's called the great wall of Ubers for a reason
However, a Mega Gar ban could be legit.. it'd get rid of walls like Chansey and Blissey, something Ghost can never seem to do.