Weaknesses 2: Fighting and Fire, Fire is a 4x weakness. Fighting and Fire are some of the most common offensive moves.
Resistances 10: Water, Normal, Electric, Psychic, Grass, Rock, Steel, Ghost, Dragon, and Steel, Grass is a 4x resistance. Rock resistance also means Stealth-rock resistance.
Immunity 1: Poison, immunity to Toxic is nice
Stat review: High Defense and S.Defense, good Attack, and decent HP. Low S.Attack and pathetic speed stat.
Movepool: A very good Walling and Tank movepool
Crippling ability: Good, usually does so with Thunder-wave or Leech-seed
Competitive usability: He is one of the most used Pokemon in competitive.
I have found this set most effective.
Item: Leftovers or Rocky-helmet
EVs: 252 Defense, 200 S.Defense, 58 Attack
Leech-seed: Healing and damaging
Stealth-rock or Spikes: Entry hazard
Weaknesses 2: Dark and Ghost. These are common offensive moves.
Resistances 2: Poison and Bug. Poison is not a very common offensive type but Bug is fairly common
Immunities 2: Fighting and Normal. Fighting is one of the most common offensive move types and Normal is used frequently for neutral damage.
Stat review: HUGE Defense, and High S.Defense and S.Attack that can be boosted by Calm-mind. Low Hp, and Attack, Pathetic speed.
Movepool: Good for walling and Tanking
Crippling ability: Will-o-wisp is very useful
Competitive usability: One of the best UU Walls and can also be used in OU.
Set: There are lots, try here: http://pokemondb.net/pokebase/13549/what-is-a-good-moveset-for-cofagrigus