I agree with AM that Mega-Altaria is a bigger threat to stall as opposed to Megagross. Rather, I should say that Mega-Altaria HAS the potential to be a bigger threat to stall the Megagross due to Roost which grants it longevity despite hazards, and due to the potential combination of Heal Bell + Dragon Dance and mixed sets. Mega-Altaria is, by essence, more of a type based matchup than dual STABs+Grass Knot+Hammer Arm Megagross because you are forced to handle it differently depending on the set that it is running, while Megagross can just be whithered and eliminated, even with the anti Stall set.
Stalls answers to Altaria consist of:
Unaware Clefable misses out on the OHKO to Altaria with Moon Blast while getting 2HKOd in the process. However, the Altaria user can easily switch out of this and once again begin boosting on something like Sableye or Chansey, especially if Facade is being run over Frustration or Double-Edge.
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 160 Def Clefable: 216-255 (54.8 - 64.7%) -- guaranteed 2HKO after Leftovers recovery
0 SpA Clefable Moonblast vs. 64 HP / 0 SpD Mega Altaria: 188-224 (61.2 - 72.9%) -- guaranteed 2HKO after Stealth Rock
This is a very good answer to DD Altaria, as it can just barely survive the 2HKO and can Toxic stall it to death. However, you better keep it status and Knock Off free and you better not choke and get critted. However, Facade Altaria can break through Quagsire on the switch.
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 252+ Def Quagsire: 162-192 (41.1 - 48.7%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
192+ Atk Pixilate Mega Altaria Facade (140 BP) vs. 252 HP / 252+ Def Quagsire: 222-262 (56.3 - 66.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
This is probably the best answer that stall has to Altaria. However, it loses to the mixed set after one switch in and losses to the very rare specially biased set 100% of the time.
0 SpA Mega Altaria Fire Blast vs. 252 HP / 120 SpD Amoonguss: 180-212 (41.6 - 49%) -- 14.8% chance to 2HKO after Stealth Rock and Black Sludge recovery
Skarmory to phaze it out to deal with it later, or it can stop a set up if the very rare Iron Head is run if Skarmory is specially defensive. However, Skarmory still loses to the mixed set.
0 Atk Skarmory Iron Head vs. 64 HP / 0 Def Mega Altaria: 134-158 (43.6 - 51.4%) -- 98.4% chance to 2HKO after Stealth Rock
0 Atk Skarmory Brave Bird vs. 64 HP / 0 Def Mega Altaria: 100-118 (32.5 - 38.4%) -- guaranteed 3HKO after Stealth Rock
0 SpA Mega Altaria Fire Blast vs. 252 HP / 4 SpD Skarmory: 228-270 (68.2 - 80.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
This is a great answer to Altaria, but it lacks recovery and Altaria can hit it on the switch and run away from the Gyro Ball,
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 0 Def Bronzong: 89-105 (26.3 - 31%) -- 80.5% chance to 4HKO after Stealth Rock and Leftovers recovery
4 Atk Bronzong Gyro Ball (92 BP) vs. 64 HP / 0 Def Mega Altaria: 168-198 (54.7 - 64.4%) -- guaranteed 2HKO after Stealth Rock and poison damage
4 Atk Bronzong Gyro Ball (138 BP) vs. 64 HP / 0 Def Mega Altaria: 252-296 (82 - 96.4%) -- 62.5% chance to OHKO after Stealth Rock
4 Atk Bronzong Gyro Ball (150 BP) vs. 64 HP / 0 Def Mega Altaria: 270-320 (87.9 - 104.2%) -- guaranteed OHKO after Stealth Rock
At full HP, Ferrothorn can always win 1v1 against every set not named specially biased. However, the mixed set still handles him well.
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 88+ Def Ferrothorn: 68-81 (19.3 - 23%) -- possible 6HKO after Stealth Rock and Leftovers recovery
0 SpA Mega Altaria Fire Blast vs. 252 HP / 168 SpD Ferrothorn: 264-312 (75 - 88.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
0 Atk Ferrothorn Gyro Ball (145 BP) vs. 64 HP / 0 Def Mega Altaria: 272-324 (88.5 - 105.5%) -- guaranteed OHKO after Stealth Rock
Specially defensive Excadrill can check Altaria, but still loses to Earthquake.
192+ Atk Mega Altaria Earthquake vs. 252 HP / 0 Def Excadrill: 306-362 (72.1 - 85.3%) -- guaranteed 2HKO after Stealth Rock
0 Atk Excadrill Iron Head vs. 64 HP / 0 Def Mega Altaria: 206-246 (67.1 - 80.1%) -- guaranteed 2HKO after Stealth Rock and poison damage
Same story as Excadrill.
192+ Atk Mega Altaria Earthquake vs. 252 HP / 4 Def Jirachi: 204-240 (50.4 - 59.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+1 192+ Atk Mega Altaria Earthquake vs. 252 HP / 4 Def Jirachi: 304-358 (75.2 - 88.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
0 Atk Jirachi Iron Head vs. 64 HP / 0 Def Mega Altaria: 158-188 (51.4 - 61.2%) -- guaranteed 2HKO after Stealth Rock
Now, as far as stall breakers go, I feel like Thundurus, Mega-Heracross, and Mega-Pinsir also deserve a mention as they can tear apart stall teams to the point where they can no longer function with their lost partners.
Thundurus @ Life Orb
Ability: Defiant
EVs: 76 Atk / 180 Spa / 252 Spe
Naive Nature
- Knock Off
- Superpower
- Thunderbolt
- Grass Knot/Psychic/Taunt
There is nothing on stall that can safely switch in on this, and even the worse of players can at least secure one kill with Wall Breaker Thundurus.
76 Atk Life Orb Thundurus Knock Off (97.5 BP) vs. 4 HP / 252+ Def Eviolite Chansey: 146-172 (22.7 - 26.7%) -- guaranteed 4HKO after Stealth Rock
76 Atk Life Orb Thundurus Superpower vs. 4 HP / 252+ Def Eviolite Chansey: 359-424 (55.9 - 66%) -- guaranteed 2HKO after Stealth Rock
76 Atk Life Orb Thundurus Superpower vs. 4 HP / 252+ Def Chansey: 536-632 (83.4 - 98.4%) -- 75% chance to OHKO after Stealth Rock
180 SpA Life Orb Thundurus Thunderbolt vs. 252 HP / 4 SpD Skarmory: 471-556 (141 - 166.4%) -- guaranteed OHKO
180 SpA Life Orb Thundurus Grass Knot (120 BP) vs. 252 HP / 112 SpD Hippowdon: 356-421 (84.7 - 100.2%) -- 43.8% chance to OHKO after Stealth Rock
180 SpA Life Orb Thundurus Grass Knot (80 BP) vs. 252 HP / 4 SpD Quagsire: 593-702 (150.5 - 178.1%) -- guaranteed OHKO
180 SpA Life Orb Thundurus Psychic vs. 252 HP / 120 SpD Amoonguss: 247-291 (57.1 - 67.3%) -- guaranteed 2HKO after Stealth Rock and Black Sludge recovery
180 SpA Life Orb Thundurus Psychic vs. 252 HP / 0 SpD Mega Venusaur: 203-239 (55.7 - 65.6%) -- guaranteed 2HKO after Stealth Rock
Heracross @ Heracronite
Ability: Guts > Skill Link
EVs: 252 Attack / 252 Spe / 4 Spd
Adamant Nature
- Pin Missle/Mega Horn
- Close Combat
- Rock Blast/Bullet Seed
- Bullet Seed/Swords Dance/Substitute
This thing breaks stall like nobodies business. It has the ability to 1/2HKO every switch in, and Scarf Gothitelle can only revenge a healthy Heracross if it is at -1.
252+ Atk Mega Heracross Close Combat vs. 252 HP / 252+ Def Skarmory: 160-189 (47.9 - 56.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+2 252+ Atk Mega Heracross Close Combat vs. 252 HP / 252+ Def Skarmory: 319-376 (95.5 - 112.5%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Pin Missile (5 hits) vs. 252 HP / 252+ Def Cresselia: 390-460 (87.8 - 103.6%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 252+ Def Quagsire: 640-760 (162.4 - 192.8%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 144+ Def Hippowdon: 280-330 (66.6 - 78.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Mega Heracross Pin Missile (5 hits) vs. 252 HP / 252+ Def Mega Sableye: 185-225 (60.8 - 74%) -- guaranteed 2HKO after Stealth Rock
Pinsir @ Pinsirite
Ability: Hyper Cutter > Aerilate
EVs: 252 Attack / 252 Spe / 4 Spd
Jolly Nature
- Close Combat/Earthquake
- Frustration
- Quick Attack
- Swords Dance
While Pinsir does require Skarmory to be broken or eliminated, Stall pretty much loses something every time that Pinsir is brought out on any specially defensive mon, as nothing can safely switch in to him.
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Unaware Quagsire: 198-234 (50.2 - 59.3%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Mega Sableye: 153-181 (50.3 - 59.5%) -- guaranteed 2HKO after Stealth Rock
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Clefable: 217-256 (55 - 64.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Cresselia: 157-186 (35.3 - 41.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 4 HP / 252+ Def Eviolite Chansey: 328-387 (51 - 60.2%) -- guaranteed 2HKO after Stealth Rock
252 Atk Mega Pinsir Earthquake vs. 252 HP / 0 Def Jirachi: 248-294 (61.3 - 72.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 144+ Def Hippowdon: 174-205 (41.4 - 48.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
If this thing manages to get a burn free Swords Dance, it's basically over late game when most walls won't be at near max HP.
Stalls answers to Altaria consist of:
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 160 Def Clefable: 216-255 (54.8 - 64.7%) -- guaranteed 2HKO after Leftovers recovery
0 SpA Clefable Moonblast vs. 64 HP / 0 SpD Mega Altaria: 188-224 (61.2 - 72.9%) -- guaranteed 2HKO after Stealth Rock
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 252+ Def Quagsire: 162-192 (41.1 - 48.7%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
192+ Atk Pixilate Mega Altaria Facade (140 BP) vs. 252 HP / 252+ Def Quagsire: 222-262 (56.3 - 66.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
0 SpA Mega Altaria Fire Blast vs. 252 HP / 120 SpD Amoonguss: 180-212 (41.6 - 49%) -- 14.8% chance to 2HKO after Stealth Rock and Black Sludge recovery
0 Atk Skarmory Iron Head vs. 64 HP / 0 Def Mega Altaria: 134-158 (43.6 - 51.4%) -- 98.4% chance to 2HKO after Stealth Rock
0 Atk Skarmory Brave Bird vs. 64 HP / 0 Def Mega Altaria: 100-118 (32.5 - 38.4%) -- guaranteed 3HKO after Stealth Rock
0 SpA Mega Altaria Fire Blast vs. 252 HP / 4 SpD Skarmory: 228-270 (68.2 - 80.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 0 Def Bronzong: 89-105 (26.3 - 31%) -- 80.5% chance to 4HKO after Stealth Rock and Leftovers recovery
4 Atk Bronzong Gyro Ball (92 BP) vs. 64 HP / 0 Def Mega Altaria: 168-198 (54.7 - 64.4%) -- guaranteed 2HKO after Stealth Rock and poison damage
4 Atk Bronzong Gyro Ball (138 BP) vs. 64 HP / 0 Def Mega Altaria: 252-296 (82 - 96.4%) -- 62.5% chance to OHKO after Stealth Rock
4 Atk Bronzong Gyro Ball (150 BP) vs. 64 HP / 0 Def Mega Altaria: 270-320 (87.9 - 104.2%) -- guaranteed OHKO after Stealth Rock
192+ Atk Pixilate Mega Altaria Return vs. 252 HP / 88+ Def Ferrothorn: 68-81 (19.3 - 23%) -- possible 6HKO after Stealth Rock and Leftovers recovery
0 SpA Mega Altaria Fire Blast vs. 252 HP / 168 SpD Ferrothorn: 264-312 (75 - 88.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
0 Atk Ferrothorn Gyro Ball (145 BP) vs. 64 HP / 0 Def Mega Altaria: 272-324 (88.5 - 105.5%) -- guaranteed OHKO after Stealth Rock
192+ Atk Mega Altaria Earthquake vs. 252 HP / 0 Def Excadrill: 306-362 (72.1 - 85.3%) -- guaranteed 2HKO after Stealth Rock
0 Atk Excadrill Iron Head vs. 64 HP / 0 Def Mega Altaria: 206-246 (67.1 - 80.1%) -- guaranteed 2HKO after Stealth Rock and poison damage
192+ Atk Mega Altaria Earthquake vs. 252 HP / 4 Def Jirachi: 204-240 (50.4 - 59.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+1 192+ Atk Mega Altaria Earthquake vs. 252 HP / 4 Def Jirachi: 304-358 (75.2 - 88.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
0 Atk Jirachi Iron Head vs. 64 HP / 0 Def Mega Altaria: 158-188 (51.4 - 61.2%) -- guaranteed 2HKO after Stealth Rock
Now, as far as stall breakers go, I feel like Thundurus, Mega-Heracross, and Mega-Pinsir also deserve a mention as they can tear apart stall teams to the point where they can no longer function with their lost partners.
Thundurus @ Life Orb
Ability: Defiant
EVs: 76 Atk / 180 Spa / 252 Spe
Naive Nature
- Knock Off
- Superpower
- Thunderbolt
- Grass Knot/Psychic/Taunt
There is nothing on stall that can safely switch in on this, and even the worse of players can at least secure one kill with Wall Breaker Thundurus.
76 Atk Life Orb Thundurus Knock Off (97.5 BP) vs. 4 HP / 252+ Def Eviolite Chansey: 146-172 (22.7 - 26.7%) -- guaranteed 4HKO after Stealth Rock
76 Atk Life Orb Thundurus Superpower vs. 4 HP / 252+ Def Eviolite Chansey: 359-424 (55.9 - 66%) -- guaranteed 2HKO after Stealth Rock
76 Atk Life Orb Thundurus Superpower vs. 4 HP / 252+ Def Chansey: 536-632 (83.4 - 98.4%) -- 75% chance to OHKO after Stealth Rock
180 SpA Life Orb Thundurus Thunderbolt vs. 252 HP / 4 SpD Skarmory: 471-556 (141 - 166.4%) -- guaranteed OHKO
180 SpA Life Orb Thundurus Grass Knot (120 BP) vs. 252 HP / 112 SpD Hippowdon: 356-421 (84.7 - 100.2%) -- 43.8% chance to OHKO after Stealth Rock
180 SpA Life Orb Thundurus Grass Knot (80 BP) vs. 252 HP / 4 SpD Quagsire: 593-702 (150.5 - 178.1%) -- guaranteed OHKO
180 SpA Life Orb Thundurus Psychic vs. 252 HP / 120 SpD Amoonguss: 247-291 (57.1 - 67.3%) -- guaranteed 2HKO after Stealth Rock and Black Sludge recovery
180 SpA Life Orb Thundurus Psychic vs. 252 HP / 0 SpD Mega Venusaur: 203-239 (55.7 - 65.6%) -- guaranteed 2HKO after Stealth Rock
Heracross @ Heracronite
Ability: Guts > Skill Link
EVs: 252 Attack / 252 Spe / 4 Spd
Adamant Nature
- Pin Missle/Mega Horn
- Close Combat
- Rock Blast/Bullet Seed
- Bullet Seed/Swords Dance/Substitute
This thing breaks stall like nobodies business. It has the ability to 1/2HKO every switch in, and Scarf Gothitelle can only revenge a healthy Heracross if it is at -1.
252+ Atk Mega Heracross Close Combat vs. 252 HP / 252+ Def Skarmory: 160-189 (47.9 - 56.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+2 252+ Atk Mega Heracross Close Combat vs. 252 HP / 252+ Def Skarmory: 319-376 (95.5 - 112.5%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Pin Missile (5 hits) vs. 252 HP / 252+ Def Cresselia: 390-460 (87.8 - 103.6%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 252+ Def Quagsire: 640-760 (162.4 - 192.8%) -- guaranteed OHKO after Stealth Rock
252+ Atk Mega Heracross Bullet Seed (5 hits) vs. 252 HP / 144+ Def Hippowdon: 280-330 (66.6 - 78.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Mega Heracross Pin Missile (5 hits) vs. 252 HP / 252+ Def Mega Sableye: 185-225 (60.8 - 74%) -- guaranteed 2HKO after Stealth Rock
Pinsir @ Pinsirite
Ability: Hyper Cutter > Aerilate
EVs: 252 Attack / 252 Spe / 4 Spd
Jolly Nature
- Close Combat/Earthquake
- Frustration
- Quick Attack
- Swords Dance
While Pinsir does require Skarmory to be broken or eliminated, Stall pretty much loses something every time that Pinsir is brought out on any specially defensive mon, as nothing can safely switch in to him.
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Unaware Quagsire: 198-234 (50.2 - 59.3%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Mega Sableye: 153-181 (50.3 - 59.5%) -- guaranteed 2HKO after Stealth Rock
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Clefable: 217-256 (55 - 64.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 252+ Def Cresselia: 157-186 (35.3 - 41.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 4 HP / 252+ Def Eviolite Chansey: 328-387 (51 - 60.2%) -- guaranteed 2HKO after Stealth Rock
252 Atk Mega Pinsir Earthquake vs. 252 HP / 0 Def Jirachi: 248-294 (61.3 - 72.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Mega Pinsir Return vs. 252 HP / 144+ Def Hippowdon: 174-205 (41.4 - 48.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
If this thing manages to get a burn free Swords Dance, it's basically over late game when most walls won't be at near max HP.