Moves
Dazzling Gleam is an excellent coverage move for Gastly, hitting Fighting- and Dark-types quite hard. However, the main function of Dazzling Gleam on this set is to give Gastly access to Twinkle Tackle, a powerful Z-Move that OHKOes Mienfoo, certain Timburr sets, and Vullaby after Stealth Rock damage. Thunder can be used instead to give Gastly a good chance to beat Alolan Grimer switchins in addition to taking out Vullaby. Sludge Bomb and Shadow Ball are powerful STAB attacks with good coverage, especially against foes such as Snivy, Spritzee, and Pumpkaboo-XL. Substitute helps Gastly protect itself from a single move, lets it avoid Sucker Punch and status moves such as Foongus's Spore, and lets Gastly avoid having to predict a switch. Hidden Power Fighting can also be used to hit Pawniard, a Pokemon that otherwise walls Gastly.
Set Details
Fairium Z lets Gastly use Twinkle Tackle to surprise some of its checks, such as Vullaby, Mienfoo, and Timburr, and deal heavy damage. A Timid nature and 196 Speed EVs are used to maximize Gastly's Speed and let it outspeed Mienfoo, Snivy, and Cottonee. 196 Special Attack EVs let Gastly do a fair amount of damage. The rest of Gastly's EVs are put into its defenses to let it survive for as long as possible. Levitate gives Gastly an immunity to Ground-types moves, allowing it to switch in slightly easier against certain Pokemon such as Choice Scarf Mudbray and Hippopotas. If using Hidden Power Fighting, Gastly should use an EV spread of 40 Def / 200 SpA / 200 Spe to maximize Special Attack and Speed.
Usage Tips
To properly utilize Twinkle Tackle, it is a good idea to try and bait in threats Gastly can KO with it, namely Timburr, Mienfoo, and Vullaby. Before doing this, however, it is usually best to scout how your opponent will react to Gastly, as Twinkle Tackle can only be used once per battle. This usually consists of checking what usually switches into Gastly and what moves said Pokemon usually uses. It's best not to attack before using Twinkle Tackle, as this would reveal that Gastly lacks a Life Orb, leading your opponent to most likely believe it is either Choice Scarf or Fairium Z. This is especially important if the opponent has something Gastly can lure in. Don't be afraid to attack afterwards, however, as Gastly can still do a lot without the element of surprise. Due to Gastly's low bulk, it is generally good to not switch Gastly into unresisted attacks, and it's preferred to get Gastly in through a U-turn or Volt Switch or after one of its teammates has fallen. Substitute should be used on a predicted switch and against Sucker Punch users to safely protect Gastly. It can also be used to avoid status from certain Pokemon such as Spore Foongus. Be sure to always avoid being in against Pursuit trappers, such as Alolan Grimer. It is also best that Gastly is only used when it can ensure a KO on a foe, as it is too frail to take nearly any damage.
Team Options
Note that Twinkle Tackle Gastly should be used on teams that appreciate a lure to Timburr, Mienfoo, or Vullaby, as if teams don't need this, Life Orb Gastly would work better. Pokemon that appreciate the removal of Fighting-types and Vullaby, such as Scraggy and Carvanha, appreciate Gastly's ability to lure in and KO said threats. Abra in particular appreciates Twinkle Tackle's ability to remove Vullaby and severely weaken Alolan Grimer and Pawniard. Gastly greatly appreciates Stealth Rock support from setters such as Pawniard, Ferroseed, Onix, and Dwebble to help it break through more Pokemon, and in return, Gastly can block Rapid Spin for them. Fighting-types, namely Mienfoo and Timburr, are very useful to help Gastly beat Dark-types, Pawniard in particular, as well as many using Knock Off to cripple foes, and Gastly can deal with Fairy-types in return. Slow pivots, namely Mienfoo, Chinchou, and Vullaby, can help Gastly get onto the field without taking any damage from attacks.
