Gengar is flat out terrifying, not only in terms of design, but in how immensely powerful the Pokemon is.
Since its introduction in Generation I, Gengar has always done the same thing in every Pokemon game. It's faster than everyone and uses incredibly strong attacks to decimate opponents.
At 110 base Speed, Gengar moves first most of the time, and it hits with a 130 Special Attack. In Pokemon Sword and Shield, Gengar’s capabilities grew tenfold because it got access to more moves through TMs and TRs.
Players who like to participate in Max Raid battles frequently will benefit when they have TRs for Energy Ball, Thunderbolt, Psychic and similar moves to teach Gengar early on. This Pokemon can become a destructive force with this moveset.
Note: This article is subjective and reflects the opinion of the writer.
The best moveset for Gengar in Pokemon Sword and Shield
The idea behind this moveset is to give Gengar a boost so that it gets in a position to obliterate everything in its way. If Gengar is faster than everybody and his Special Attack is boosted, there really shouldn't be anything that can survive his attacks besides Blissey.
Nasty Plot is the Christmas present Gengar has been asking for throughout seven generations of Pokemon. The one major thing that Gengar was always missing in its movepool was a decent way to stat boost.
An easy fix to this issue used to be giving Gengar Choice Specs, but that isn’t exactly the most abundant item in most Pokemon games. Nasty Plot raises the Pokemon’s Special Attack by two stages.
At that point, what Pokemon is going to take a Shadow Ball? Normal-type Pokemon would be immune, Dark-type Pokemon would resist even though they would take serious damage. Just about anything else would fold to Gengar.
Shadow Ball is the no-brainer of the set. An 80 base power Ghost-type move, Shadow Ball can drop heavy damage on a wide variety of Pokemon. With its high Special Attack stat, Gengar has one of the strongest Shadow Balls of any Pokemon in the game. It offers very consistent damage to teams without a Normal-type Pokemon.
Since Normal-types are a big issue for Gengar, pairing it with another strong move is necessary to damage those Pokemon. It may not be super effective, but Sludge Wave gets the same type of attack boost and will KO most Normal-type Pokemon after a Nasty Plot boost. Sludge Wave also allows Gengar to deal with common Pokemon like Sylveon, Gardevoir, Eldegoss and Clefable.
Dazzling Gleam is a secret weapon for Dark-type Pokemon. Ideally, Gengar would Nasty Plot in front of a different Pokemon, and then be boosted for whatever Dark-type is in the back. It won’t exactly beat Piers’ Dark-type Gym on its own, but it could take out a Pokemon or two.
Another big option for this slot is Focus Blast as a way to deal with the Normal-type immunity. At 70% accuracy, though, this move is going to miss quite often. It’s nice to hit annoyances like Blissey, Indeedee and Snorlax, but a player could always just switch to a different Pokemon.