May I offer my set; specially defensive Chesnaught
Chesnaught @ Leftovers
Ability:- Bulletproof
EVs:- 252 HP / 4 Def / 252 SDef
Nature:- Impish (+Def -SAtk)
- Leech Seed
- Spiky Shield
- Hammer Arm
- Synthesis / Earthquake
Chesnaught is normally seen as an exceptionally bulky physical wall that stops pokemon like Excadrill, Tyranitar, Bisharp etc while also being able to switch into weak resisted attacks on the special side like 4 SAtk Rotom-W Volt Switch. However, I have found that Chesnaught is still able to beat the physical threats it wants to take on even after a boost, as long as it stays relatively healthy, while also being able to take on select special attacking pokemon whose STAB attacks it resists. With special defence investment, Chesnaught becomes able to take on things like Choice Specs Keldeo as long as rain isn't present, to give an example of its special bulk. The calcs all show the most powerful moves that pokemon can use against Chesnaught:
252+ Atk Mold Breaker Excadrill Iron Head vs. 252 HP / 4+ Def Chesnaught: 114-135 (30 - 35.5%) -- 0.1% chance to 3HKO after Stealth Rock and Leftovers recovery
252+ Atk Landorus-T Earthquake vs. 252 HP / 4+ Def Chesnaught: 75-88 (19.7 - 23.1%) -- possible 6HKO after Stealth Rock and Leftovers recovery
252+ Atk Mega Scizor U-turn vs. 252 HP / 4+ Def Chesnaught: 108-127 (28.4 - 33.4%) -- guaranteed 4HKO after Stealth Rock and Leftovers recovery
252+ Atk Choice Band Scizor U-turn vs. 252 HP / 4+ Def Chesnaught: 144-171 (37.8 - 45%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
+2 252+ Atk Life Orb Bisharp Iron Head vs. 252 HP / 4+ Def Chesnaught: 277-328 (72.8 - 86.3%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+1 252+ Atk Mega Tyranitar Fire Punch vs. 252 HP / 4+ Def Chesnaught: 246-290 (64.7 - 76.3%) -- guaranteed 2HKO after Stealth Rock, sandstorm damage, and Leftovers recovery
+1 252+ Atk Mold Breaker Mega Gyarados Ice Fang vs. 252 HP / 4+ Def Chesnaught: 204-240 (53.6 - 63.1%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
4 SpA Rotom-W Hydro Pump vs. 252 HP / 252 SpD Chesnaught: 59-69 (15.5 - 18.1%) -- possible 8HKO after Stealth Rock and Leftovers recovery
252 SpA Thundurus Hidden Power Ice vs. 252 HP / 252 SpD Chesnaught: 122-144 (32.1 - 37.8%) -- 30.5% chance to 3HKO after Stealth Rock and Leftovers recovery
252 SpA Choice Specs Keldeo Icy Wind vs. 252 HP / 252 SpD Chesnaught: 170-202 (44.7 - 53.1%) -- 26.6% chance to 2HKO after Stealth Rock and Leftovers recovery
252 SpA Aegislash-Blade Flash Cannon vs. 252 HP / 252 SpD Chesnaught: 138-163 (36.3 - 42.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
As can be seen, Chesnaught is bulky enough on both sides to be a mixed wall. With Earthquake, Chesnaught can check Aegislash, if that isn't necessary then Synthesis is preferable to keep Chesnaught healthy at times where Leech Seed + Leftovers with Spiky Shield isn't enough. It happens much more frequently when Chesnaught is taking on threats on both sides. As opposed to being an out-and-out wall, I have found that Chesnaught tends to play more like a pivot, switching into a weak resisted attack, pulling off a Leech Seed and Spiky Shield to heal and deal some damage, then switching out.
One question is why use this over Mega Venusaur? Well it doesn't take up your Mega Evolution spot for starters. It also check the aforementioned boosted physical threats that Mega Venusaur is less able to, Hammer Arm does huge amounts of damage to Excadrill, Bisharp, (Mega) Tyranitar, Mega Gyarados that Giga Drain and an Earthquake lacking STAB can't. With Leech Seed and Spiky Shield, Chesnaught is able to deal residual damage quickly, allowing it to check VoltTurn reliably. Notice how all of (Mega) Scizor, Rotom-W and Landorus-T are up there. Mega Venusaur is unable to wear them down so quickly, despite being able to take their attacks. This applies to offence in general really, wearing them down gradually while taking little net damage in return. In short, while Mega Venusaur is passive and simply refuses to die, Chesnaught actually deals residual damage to the team while keeping itself healthy.