I mean, you can try it, if you really want to know. The thing is, you mention that "once their ttar counter has been removed", but if you've only got one Pokemon that can deal with ttar on a team, you're gonna lost a lot of games. He's just too good. If you've beaten all their ttar counters, then why would you want to lower your speed? It just gives Pokemon that would otherwise roll over and die (if you were DDing) a chance to smack you.Im not arguing that dragon dance is superior, it definently is, however I wasnt sure if a curse tyranitar was viable, since it sill has a great HP and special defense stat. From the looks of things its wont be particularly easy to set up with him, but im going to have to give it a shot, just to see for myself. I want to see how well it does. If it gets eaten then so be it, it was in the other options section for a reason, lol. As far as regirock goes, is he used commonly? I fought one once, and it surprised the pants off me with counter and ohkoed whatever it was I tried to hit him with.
Regirock is definitely not used commonly. That doesn't mean it's bad, but it's just not as good as the commonly used mons. There are a lot of Pokemon that are still viable, but aren't used very much, due to being too niche, or being outclassed by someone else.