I have also gone back to testing Psyspam yet again despite it being generally rough. The biggest problem being speed control. My answer to fix this is ironically Rillaboom. It's the only mon that can give you priority while Psychic Terrain is up since it replaces it. Too many times have I had some setup sweeper or boosted mon come in and tear through my PT teams with no way to immediately respond. The solution being Grassy Terrain legitimately hurts my soul. But once I discarded my useless sentimentality, I found it to be quite useful so far in limited testing.
Rillaboom helps some of the worst matchups. Like how rain Barraskewda outspeeds everything you can run, including Hawlucha. But Rillaboom turns the tables in hilarious fashion. It also helps the Hamurott matchup a ton. Leading in general becomes far easier because teams that matchup well into the classic Indeedee lead now have to worry about different lead options. Generally, it just fixes so many weaknesses to actually have usable priority on this archetype.
I have decided I don't like Hawlucha on Psychic Terrain. It's fast, but not fast enough to actually outrun everything you would need it to. Barraskewda in the rain outruns you. BE speed Roaring Moon with a single Dragon Dance outruns you. Etc. It also needs a Swords Dance to properly revenge kill a lot of threats. If you are responding and not setting up in an advantageous position, it's a lot worse. Hawlucha simply can't solve all of speed control problems of Psychic Terrain. This is much less of an issue on Grassy Terrain.
To me, the best and most consistent sweeper for PT is Polteageist. Stored Power from Shell Smash is just really good. Fighting Tera Blast and Shadow Ball are nearly perfect complimentary coverage. Even if it doesn't get a sweep, you can generally punch holes in the opposing team.
This brings me to an unlikely core of Indeedee, Polteageist, and Rillaboom. Kinda strange, but it seems way more promising than any Psychic Terrain core I have tried before. You might ask why not just Grassy Terrain since it's a superior archetype. And to that I say, Polteageist is actually a good reason to run Psychic Terrain. You just need a team that doesn't let it down. I believe that a lot of the other conventional mons people are used to running on Psychic Terrain aren't as good, though, and that the solutions to making this archetype more consistent might lie in more out of the box solutions. Also, forcing like 4 RU mons onto an OU team because that's the archetype might be unwise.
Coverage wise, Fire types are almost a necessity on Psychic Terrain just because of the need to hit the metal birds and many Steel types. I am very down on Armarouge, though, since triggering the weakness policy is extremely gimmicky and not reliable enough. HBD just makes it weaker. It is hard to make it consistent.
I have also tested Blaziken. Blaziken has a similar issue to Hawlucha in that it takes too long to get going and it hates facing the boosted speed tiers that are too fast for it. I think there is maybe a place for it on very specific teams, but Psychic Terrain probably ain't it.
Cinderace strikes me as a really decent option since it is fast and can help with the hazard issue. You can just come in with immediate speed and power. I think Psyspam teams tend to lean so heavy into the HO factor that they simply don't have much immediate power work with.
What I am currently testing is Psychic Seed Gouging Fire. The results so far have been mixed. With just Psychic Seed, it was able to survive a +1 Tera Ground Volc TB. So far, it can't get setup enough. The survivability is good. A decent amount of mons outspeed it at +1, so you really need to be at +2 most of the time. The boosted metagame can sometimes outspeed you even at + 2. I am pretty sure I could be using a more optimal set, but I don't know if I should lean more towards an offensive set or even more bulk.
I don't think a Tera Blast ban would happen, but if it does, it would nerf Polteageist to the point where Psychic Terrain is probably irreversibly irrelevant again instead of just mostly so. I also found TB is very helpful on Indeedee since it is a decent base power Normal STAB that can also become emergency coverage. The lack of normal attackers in the tier to use TB is maybe something to look at in general. We might be able to make some niche options work in certain team structures.
