Cofagrigus: the coffin pokemon that eats people. Cool stats, cool typing, too bad it misses some moves that like every other ghost type gets (no Pain Split... SERIOUSLY?)
Set Name: This bulky coffin will eat your soul
Ability: Mummy
Item: Leftovers
Nature: Bold
Evs: 252 Hp, 252 Def, 4 SpDef
-Will-o-wisp
-Hex/Shadow Ball
-Curse/Haze
-Rest/Disable
Cofagrigus has an insane defence stat and ghost typing, so it can sponge phisical hits quite well. Will-o-wisp cripples completely any non-guts phisical sweeper, Hex gets 100 BP on a statused opponent so comboes very well with Will-o-wisp. Shadow Ball is still an option if you fear pokemon immune to burn or if you don't want to need a turn to status the opponent before you can start attacking. Ghost type Curse is an underrated move that forces switchs like crazy and demolishes Baton Pass chains. Haze is a rare move that Cofagrigus can use nicely to stop set up sweepers. Rest is your only form of recovery and is quite necessary if you run curse. Disable can be useful since many opponents only carry one move that can actually damage Cofagrigus. For the EVs ALWAYS max HP since 58 base stat, than you can go with max defence. Also max special defence is viable, but than why not using something else like Dusknoir?
Other options
Subsitute comboes well with disable. Toxic is an alternative status affliction. Heal block works well with Toxic against pokemon with reliable recovery. Protect stalls out the residual damage and gives you more Leftovers recovery.
Power Swap can reduce your opponents attacking stats and increase yours.
Partners
A cleric makes your Rest more reliable. Blissey/Chansey are the best as they are immune to ghost while you're immune to fighting and because they are great special walls while you are a good phisical wall. They can also pass wishes. Wish passers in general aer good.
Counters
Swellow is immune to ghost, appreciates the burn and starts spamming boosted Brave Birds on everything. Houndoom is immune to burn too, resists ghosts and destroys you with a dark pulse. Chansey/Blissey can easily stall you unless you pack Toxic+Heal Block and force you to use Rest. Specially based dark types in general are great counters, so are ghost types, but they are hit hard by a ghost attack. Magic Guard Clefable completely laughs at everything you pack.
Set Name: Bulky Calm Mind
Ability: Mummy
Item: Leftovers/Chesto Berry
Nature: Bold
Evs: 252 Hp, 252 Def, 4 SpAtk
-Calm Mind
-Shadow Ball
-Hidden Power [Fighting]
-Rest/Will-o-wisp/Substitute
Cofagrigus was made to use Calm Mind: is has a monstrous defence, a nice SpAtk, perfect offensive coverage in two moves, only 2 weaknesses... just great. The only questions are abuot the last move. Rest is doable whith your monstrous defences after some Calm Minds. You can use a Chesto Berry to immediatly wake up after the set up and attempt a sweep. Otherwise, Will-o-wisp is still an option to cripple phisical threats, while Substitute works well with calm mind, since you substitute becomes almost unbreakable after some Calm Minds. For the EVs, max defence is recomended. You can invest in SpAtk, expecially with Rest-Chesto. Your defence is great even without EVs in defence.
Other options
Almost everything was listed, I guess...
Partners
Similar stuff to what was listed before.
Counters
Unlike many other special sweepers, the pink fat blobs are NOT good counters. Whithout Toxic, they can't do anything, and Rest-Chesto and Substitute varriants will win no matter what. P-hazers are great counters. Honchkrow can take you attacks and smashes you with Super Luck Night Slash. Banded Tyranitar doesn't like Hidden Power or Will-o-wisp, but smashes you with a scary powerful crunch. Mandibuzz is probably the perfect counter: it takes your moves all day long and blows you away with Whirlwind.
Whimsicott comes in as you set up and encores you into your non attacking move.
Set Name: A nasty coffin found in the trick room
Ability: Mummy
Item: Leftovers/Life Orb
Nature: Quiet
Evs: 252 Hp, 252 SpAtk, 4 SpDef
IVs: 2 Spe and Atk, 30 Def, Sp Atk, SpDef , 31 Hp
-Trick Room
-Nasty Plot
-Shadow Ball
-Hidden Power [Fighting]
This is a Trick Room sweeper, and a very good one. Your Speed is 60, so in Trick Room you outspeed anything faster than that. Nasty Plot doubles your attack thar reaches 632. Your last two moves give you unresisted coverage.
Max Hp to take hits, max SpAtk to murder stuff. Leftovers to last longer and set up Trick Room repeatedly, Life Orb to get more instant power. Here are given the best IVs for a 70 BP Hidden Power [Fighting] with lowest possible speed and Atk (to do less damage to youself should you hit yourself in confusion).
Other options
Almost everything was listed, I guess...
Partners
Trick Room abusers.
Counters
Mandibuzz is still the best counter ever. Honchkrow outspeeds and spells your doom with Sucker Punch. Should you try to outstall it with non attacking moves, Trick Room will be outstalled too and he will just Night Slash or Brave Bird you. Bisharp does the same thing, but is x4 weak to Hidden Power. Whimsicott comes in as you set up and encores you into your non attacking move.