This is my first ever setup for a Pokémon, as when I jump into competitive battling I plan to start in the NU tier, so be gentle! 
[SET]
name: ContraTank
move 1: Shell Smash
move 2: Encore / Power Split
move 3: Toxic
move 4: Rest
item: Rocky Helmet / Leftovers
ability: Contrary
nature: Impish / Bold
evs: 252 HP / 228 SpD / 30 Def
ivs: 0 Atk / 0 SpA
[SET COMMENTS]
Pros:
Cons:
[ADDITIONAL COMMENTS]


[SET]
name: ContraTank
move 1: Shell Smash
move 2: Encore / Power Split
move 3: Toxic
move 4: Rest
item: Rocky Helmet / Leftovers
ability: Contrary
nature: Impish / Bold
evs: 252 HP / 228 SpD / 30 Def
ivs: 0 Atk / 0 SpA
[SET COMMENTS]
- With a defense boosting nature and the EV spread, Shuckle will have 244 HP, 553 Defense and 553 Special Defense
- With it's Contrary ability Shell Smash will raise both of Shuckle's already preposterous defenses by on stage each turn from 553 (0) > 829 (1) > 1105 (2) all the way to 2212 (6)
- This gives him higher Defense than Regirock and higher Special Defense than Regice, all on one Pokémon
- If you can catch your opponent off guard with an encore you may be able to force them to switch out giving you a free turn for Shell Smash, lock them into a pathetically low damaging attack or force them to keep setting up themselves.
- If you use Power Split, you can burden even the most powerful of sweepers by halving their attack stats
- If you use Power Split, it is advised to use Bold or Impish natures to further hinder physical or special attackers
- It is advised that you use the Bold nature in order to further hinder physical attackers, as they are Shuckles primary threats
- Using Rampardos as a great example (highest attack in the tier), he can have a maximum of 471 attack, powersplit creates an average between both Shuckle's and Rampardos' attack stats which is calculated as 471 + 13 / 2 = 242. That is 87 points lower than an attack hindering natured Rampardos with 0 EVs.
- After six turns you will have the most defensive Pokémon in the game
- The natures specified allow Shuckle to have a large pool of HP whilst bolstering his impressive 230 base Defense & Special Defense stats
- If you choose Rocky Helmet you will stall and recoil any physical attacker in the tier into their graves
- With leftovers you will get some considerable bonus bulk, but well timed Rests can render the item useless when your opponent could be receiving more damage than they can deal through Rocky Helmet recoil ontop of Toxic
- With both defense stats well above 2000 even a Life Orb, +6 Zangoose will struggle to take it down
- With Life Orb, Toxic & Rocky Helmet damage building up each turn it can force even the mightiest of physical attackers to switch out before they kill themselves flailing against Shuckle's massive bulk
Pros:
- Highest defenses in the game
- Ability to fully heal every 3 turns
- Capable of causing a ton of damage-over-time with Toxic/Rocky Helmet to physical attackers
- Frustrating to play against, may fluster and put your opponent off their game
- With Power Split, Shuckle can render any offensive Pokémon completely useless
- Shuckle can force his opponent to attack his 2,000+ strong defenses with halved offense
- A huge underdog story with every battle!
Cons:
- Quite luck based, critical hits/supereffective attacks can destroy the strategy
- Susceptible to being set-up bait
- Less offense against special attackers
- Extremely weak to Rampardos, Kingler, Armaldo, Metang and other common, offensive Rock/Steel/Water Pokémon
- Higher potential meta-power but less reliable than a Eviolite Wynaut
- Unable to setup Toxic on Steel/Poison types, completely incapable of damaging Steel/Poison special attackers
- Completely walled and overpowered by Corsola which is a far inferior tank
[ADDITIONAL COMMENTS]