Regirock

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.