I’m grateful for the likes of PKMNcast for creating Tera Raid Pokémon guides, for event Pokémon and general raids. But there is also a website called Terastal.net that offers quick lookups for any raid Pokémon. You can either filter your Pokémon by type or search manually, select the Tera Type and number of stars for the raid, and it will tell you its possible moveset, the moves’ base powers, and whether they are physical, special, or status moves. You also get a ton of other useful data about the Raid Pokémon but the best part is that you get a list of potential counter Pokémon. It’s all laid out in tables and it’s fairly easy to read and my partner and I have found great success with it because working this stuff out is a nightmare at the best of times.
I did find one potential downside: for Greninja, for example, it offered a list of good counter Pokémon but only in terms of resistances and immunities. Only one on the list offered any offensive pressure (Gastrodon) and there are plenty of options such as Klefki (which is in the list), Vaporeon, and Clodsire (the latter two weren’t in the list) that learn super effective moves to beat its Poison Tera Type. So if you pick a Pokémon with a “Very Good” score, check their moveset for any super effective moves before doing a build.
That said, check the site out and let us know how it works for you!