While Regirock appears to be an inferior Pokemon in OU due to its poor typing, which gives it weaknesses to common Grass-, Water-, Fighting-, and Ground-type attacks, it actually has a niche as an extremely bulky Curse user. Regirock has the greatest physical bulk in OU and very respectable Special Defense, especially with the boost from sandstorm. Regirock's massive bulk can help negate its bad typing and enables it to set up several Curses, Rest off any damage, and bulldoze through the opponent's team. Regirock also has decent Attack and near-perfect coverage with just Earthquake and STAB Rock Slide. To top it off, Regirock has a very handy ability in Clear Body, which stops Intimidate from reducing its Attack.
Despite these useful assets, Regirock requires serious team support to function. A Sand Stream Pokemon is necessary and a way to deal with your opponent's Water- and Grass-types is absolutely critical. Regirock also has pretty stiff competition with Tyranitar for a team slot, as it has better Attack and Special Defense and even provides its own sandstorm. Despite these somewhat disappointing setbacks, Regirock is still very destructive if properly supported and played.
The idea of this set is to come in on a Pokemon who doesn't threaten Regirock, such as Heatran, Zapdos, or Weavile, and start setting up. After a Curse or two, Regirock will be able to take even super effective physical attacks with over half of its HP remaining. Should your opponent's special attackers be gone, Regirock will become hard to stop. When Regirock is running low on health, it can just Rest off the damage, wake up instantly thanks to Chesto Berry, and attempt a sweep.
When using Regirock, it's inevitable that it will be compared to Tyranitar. Regirock has its advantages, however; it has superior Defense, lacks the 4x weakness to Fighting-type attacks, and doesn't have a weakness to Bug-type attacks. This enables it to come out on top against Gyarados, Dragonite, Lucario, and Scizor, all of whom Tyranitar loses to.Team Options & Additional Comments >>>
In OU, Regirock doesn't have too many useful other options. Regirock could run a somewhat effective tank set due to its impressive physical bulk; however, its poor defensive typing and lack of reliable recovery really hurt its usefulness in that regard. It could also attempt to run a Rock Polish set similar to Agility Metagross, but it lacks the raw power and Speed that enable Metagross to wreak havoc and hit important Speed benchmarks, respectively.
Checks and Counters
Grass- and Water-types, such as Suicune, Celebi, and Breloom, are a real pain for Regirock. Suicune and Celebi can set up on Regirock, while Breloom not only resists Earthquake and Rock Slide, but can freely set up a Substitute, put Regirock to sleep, and beat it down with its STAB attacks. Skarmory and Hippowdon can phaze Regirock without too much trouble, but can do nothing else; in a one-on-one situation, Regirock will almost always emerge victorious. Gliscor with Taunt and Toxic can counter Regirock as long as it doesn't have too many Curses under its belt when Gliscor comes in.