My first playthrough, I had a hard time with Radomos. My second playthrough, I was much better prepared and beat him on my second try.
For one, the field has some interesting quirks, to say the least. Honestly, the field is 90% the challenge here on this fight. Psychic does rock type damage and is boosted by 1.5. Whoever is your ace sweeper, should be the last one on your team, so it can get that 1.5x bump from being a queen.
I had gotten a Beldum as a wonder trade from someone, and it had become a Metagross by this point. It tanked this fight pretty well.
Forretress is another one that can wall up pretty well and responds well to the trick room, but, it has almost no offensive power whatsoever. I really don't like running Forretress unless I have access to TM06 - Toxic, which unfortunately, isn't available until later on. Golem and Steelix are other good options here as well. Slow tanks take well to this fight because of trick room. Fast sweepers tend to perform poorly for the same reason.
View chess board field here:
https://pokemon-reborn.fandom.com/wiki/Chess_Board
