I'll go back through and make the following changes:
- I forgot that Kingdra also has Swift Swim. I'll run damage calculations for that matchup, though I doubt Relicanth will stand up in such a fight.
- I'll clarify that the ExtremeSpeed Arceus matchup should only be done as a revenge kill. I had noted that Earthquake from Arceus would wreck Relicanth, but forgot to factor in that for some strange reason.
- Perhaps not, but I've seen Energy Ball more than a couple times while testing. Regardless, Deoxys-S can beat Relicanth toe-to-toe with a couple powerful Special moves if it carries the right ones and Relicanth is sufficiently damaged. Noted.
- I thought that I'd pointed out Groudon's ability to smash Relicanth to bits, but I guess I only listed the rain analysis. I'll note that.
It would seem that Ferrothorn and Genesect would need to be removed by a partnered fire type, since they both pose a threat. It is interesting that while Scarf Genesect outruns Relicanth, even max SpA Thunderbolt will only 2HKO. Thunder, while rare, is enough to kill Relicanth immediately. Countering with Head Smash will always OHKO all but the most defensive Genesect, but the recoil will finish you off. That's definitely a danger.
Obviously the main competition for a team slot is Kabutops. I'll put together a team for each of them and see where this goes. Though I suppose a dedicated rain team could use both, if you don't mind the massive grass and sun weakness.