There is a few things reguarding as useful in the game, and there’s section.
For support, the most go-to are probably altaria, with blissey/lickilicky following. Altaria is good due to c9(cloud nine) and refresh/safeguard, with 4x speed as a backup runner as well. Lickilicky is just a worser altaria due to no 4x speed. Blissey is also just a very good overall support.
As for speedrunning, most dragon flying types are the way to go. Noivern is usually the most popular, with 4x speed during clear weather (clear rock) and gets access to moonlight. Yanmega is also a really popular early game option due to speed boost.
Weather based mon is also a really big part. In sun weather, whimsicott is usually one of the more used pokemons. Gastrodon and Lumineon in rain due to 4x speed and swift swim. A-tales/Vanilluxe are also good mons to provide hail weather.
You can also refer to this Shiny hunting + PMU meta guild to learn more!