The two major doubles formats right now are VGC Regulation H and Smogon's Doubles OU. Some Pokemon not mentioned here, like Calyrex-Shadow, will probably be relevant once VGC Regulation G comes back. But for now...
Gholdengo
Gholdengo has one of the best Abilities in the game, making it immune to status. This coupled with a great typing and high Special Attack cement it as a strong force in both formats, especially when it has wide set versatility to keep the opponent guessing.
Annihilape
Annihilape pairs well with Maushold's Beat Up to power up Rage Fist. Defiant is strong in VGC thanks to the ubiquitous presence of Intimidate Pokemon like Incineroar, and Annihilape is a good Tera abuser to muscle past its checks. It's banned in Doubles OU and very strong in Regulation H.
Dragapult
Dragapult is much stronger in VGC than DOU, partly due to the former's shorter games. It's faster than nearly every other Pokemon, can break through Protect with Phantom Force, and threatens both opponents simultaneously with Dragon Darts.
Sinistcha
Sinistcha is a little better in DOU than in VGC, but it has a niche in both thanks to a robust support movepool (Rage Powder, Trick Room, Life Dew) and the bulk to take advantage of its unique traits. It's a decent redirector if you need to enable offensive threats.
There are other moderately viable Ghost types for these formats. If you don't like the options here, poke through the tiers' viability rankings until you find something that meets your needs.
VGC Regulation H Viability Rankings (Smogon)
SV Doubles OU Viability Rankings (Smogon)
