What is the difference between a Physical and Specially Defensive spread? Are you missing out on handling certain threats?
NOTE: All scenarios assume the opponent is in a position where switching out is not an option. I recognize other likely scenarios, such as the opponent predicting the Mega Aggron switch and spamming Flare Blitz, and also the implications of that should Stealth Rock be absent or present on the field. The following scenarios are just the most likely possibilities that popped into my head.
Mega Charizard X
252 HP / 252 SDEF vs. Mega Charizard X
Assume: The opponent has a Defog user and was able to remove Stealth Rock from the field. Mega Charizard X enters the field with no prior damage. He Mega Evolves, and you switch in on the Dragon Dance.
- +1 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (72.3 - 85.4%) or 249-294 damage.
- Mega Charizard X loses 83 - 98 HP in recoil damage, or ~24.7 - 29.2% of its health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard has lost 83.7 - 98.9% of its health, and Mega Aggron 72.3 - 85.4%.
- If Mega Charizard X uses Flare Blitz again, he will deal ~52 - 97 damage, and be dealt ~(17.3 - 32.3) HP or ~(5.1 - 9.6%) in recoil.
- Unfortunately, this means Charizard X will only lose (88.8 - 108.5%) - which is approximately a 1/3 chance of being able to trade Mega Aggron for Mega Charizard X (maybe slightly higher).
Assume: The opponent was unable to remove Stealth Rock from the field before switching in their Charizard. This turn, he Mega Evolves, and uses Roost, which allows you to switch in for free.
- +0 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (48.2 - 57.5%) or 166-198 damage, a 91.8% chance to 2HKO, guaranteed after Stealth Rock.
- Mega Charizard loses 55.3 - 66 HP from recoil; ~16.4 - 19.6% of its health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard X has lost 75.4 - 89.3% of its health, and Mega Aggron 48.2 - 57.5%.
- If Mega Charizard attacks again, he risks losing another 14.3 - 17.4% of its health.
- Mega Charizard takes (89.7 - 106.7%) from this encounter assuming a health Mega Aggron - which is still only about a 1/3 chance of being able to trade Mega Aggron for Mega Charizard X.
Assume: Charizard has Mega Evolved on a previous turn but was forced out by a fast threat the was capable of KO'ing it. The opponent was not able to remove Stealth Rock from the field. With the fast threat now removed, Mega Charizard X uses Dragon Dance, attempting to sweep. You switch Mega Aggron in on the Dragon Dance.
- Mega Charizard X is sitting at 75% health.
- +1 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (72.3 - 85.4%) or 249-294 damage.
- Mega Charizard X loses 83 - 98 HP in recoil damage, or ~24.7 - 29.2% of its health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard X loses this encounter due to Stealth Rock damage, Flare Blitz recoil, and Mega Aggron's Earthquake.
252 HP / 252 DEF vs. Mega Charizard X
Assume: The opponent has a Defog user and was able to remove Stealth Rock from the field. Mega Charizard X enters the field with no prior damage. He Mega Evolves, and you switch in on the Dragon Dance.
- +1 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (63.9 - 75.8%) or 220-261 damage.
- Mega Charizard X loses 73 - 87 HP in recoil damage, or ~21.8 - 25.9% of its health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard has lost 80.8 - 95.6% of its health, and Mega Aggron 63.9 - 75.8%.
- If Mega Charizard X uses Flare Blitz again, he will deal ~86 - 124 damage, and be dealt ~(28.6 - 41.3) HP or ~(8.5 - 12.3%) in recoil.
- Charizard X will only lose (89.3 - 107.9%) - only losing about ~1% more health than the specially defensive spread.
Assume: The opponent was unable to remove Stealth Rock from the field before switching in their Charizard. This turn, he Mega Evolves, and uses Roost, which allows you to switch in for free.
- +0 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (43 - 50.8%) or 148-175 damage, a 4.3% chance to 2HKO, 46.1% after Stealth Rock.
- Mega Charizard X loses 49.3 - 58.3 HP in recoil; 14.6 - 17.3% of his health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard X has lost 73.6 - 87% of its health; Mega Aggron only 43 - 50.8%.
- Mega Charizard loses 88.2 - 104.3 from this encounter; the odds of winning are in favor of Mega Aggron, who will have just enough health to guarantee a safe switch-in after your opponent kills him.
Assume: Charizard has Mega Evolved on a previous turn but was forced out by a fast threat the was capable of KO'ing it. The opponent was not able to remove Stealth Rock from the field. With the fast threat removed, Mega Charizard X uses Dragon Dance, attempting to sweep. You switch Mega Aggron in on the Dragon Dance.
- Mega Charizard X is at 75% health.
- +1 252 ATK (Jolly) Tough Claws Mega Charizard Flare Blitz: (63.9 - 75.8%) or 220-261 damage.
- Mega Charizard X loses 73 - 87 HP in recoil damage, or ~21.8 - 25.9% of its health.
- +0 Mega Aggron (Relaxed) Earthquake: (59 - 69.7%) or 176 - 208 damage.
- Mega Charizard X loses to a combination of Stealth Rock damage, Flare Blitz recoil, and Mega Aggron's Earthquake.
- Mega Aggron walks away with about ~9% more HP than the specially defensive spread.
Conclusion: vs. Mega Charizard X
There is no significant difference between the two spreads in regards to how well Mega Aggron is able to check Mega Charizard X. Both spreads require Stealth Rock to be on the field, or for Mega Charizard X to be at 75% health or less, most of (if not all of) their HP, and must switch in on the Dragon Dance / Roost, or after a kill. Physically defensive Aggron is given a little more leeway on how much he needs to guarantee he survives the encounter with +1 Jolly (83% vs. 92%), but 9% isn't enough to merit use over the Specially Defensive spread unless Mega Charizard X becomes the next Mega Kangaskhan. He is a check, not a counter.
Mega Kangaskhan
252 HP / 252 SDEF vs. Mega Kangaskhan
Assume: You have switched in on the Power-Up Punch. This variant of Mega Kangaskhan runs Fire Punch over Earthquake to deal with Ferrothorn, and has only taken 1 round of Stealth Rock damage.
- +0 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (40 Base Power): (9 - 10.7%)
- +1 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (20 Base Power): (6.9 - 8.1%)
- +2 252 ATK (Adamant) Mega Kangaskhan Fire Punch (75 Base Power): (49.7 - 58.7%)
- At this point, Mega Aggron has lost 65.6 - 77.5% of its health.
- +0 0 ATK (Relaxed) Mega Aggron Superpower (120 Base Power): (65.5 - 77.4%)
- Mega Kangaskhan wins this encounter unless Stealth Rock and 3 layers of Spikes are on the field.
- If you run Dragon Tail, you can force Kangaskhan out and potentially find an opportunity to heal Aggron up before sending him back into the fray. After two rounds of Stealth Rock damage and 1 Dragon Tail, Mega Aggron can kill Kangaskhan with Superpower.
Assume: The opposing Mega Kangaskhan players is unaware that Heavy Slam / Iron Head followed by Superpower is guaranteed to KO Mega Kangaskhan after 1 round of Stealth Rock damage. Consequently, they try to use you as an opportunity to set up a sweep.
- +0 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (40 Base Power): (9 - 10.7%)
- +1 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (20 Base Power): (6.9 - 8.1%)
- +0 0 ATK (Relaxed) Mega Aggron Heavy Slam / Iron Head (80 Base Power): (32.7 - 38.7%)
- +2 252 ATK (Adamant) Mega Kangaskhan Fire Punch (75 Base Power): (49.7 - 58.7%)
- +0 0 ATK (Relaxed) Mega Aggron Superpower (120 Base Power): (65.5 - 77.4%)
- Mega Aggron wins any encounter in which Mega Kangaskhan takes Mega Aggron on headfirst while he still has 80% of his health or more leftover. This, however, is unlikely.
252 HP / 252 DEF vs. Mega Kangaskhan
Assume: You have switched in on the Power-Up Punch. This variant of Mega Kangaskhan runs Fire Punch over Earthquake to deal with Ferrothorn, and has only taken 1 round of Stealth Rock damage.
- +0 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (40 Base Power): (7.8 - 9.5%)
- +1 252 ATK (Adamant) Mega Kangaskhan Power-Up Punch (20 Base Power): (6.1 - 7.2%)
- +2 252 ATK (Adamant) Mega Kangaskhan Fire Punch (75 Base Power): (29.6 - 34.8%)
- At this point, Mega Aggron has lost 43.5 - 51.5% of its health.
- +0 0 ATK (Relaxed) Mega Aggron Heavy Slam / Iron Head (80 Base Power): (32.7 - 38.7%)
- Mega Kangaskhan has lost 45.2 - 51.2% of its health, factoring in Stealth Rock damage.
- +0 0 ATK (Relaxed) Mega Aggron Superpower (120 Base Power): (65.5 - 77.4%)
- As long as Mega Aggron is at or near full health, physically defensive spreads will beat non-Earthquake Mega Kangaskhan 100% of the time, barring bad luck.
Conclusion:
Physically Defensive spreads counter variants of Mega Kangaskhan that do not run Earthquake, and are capable of checking the ones that do, as long as Mega Kangaskhan has taken prior damage and they are not switching in on the Power-Up Punch. By running the Specially Defensive spread, your ability to check and counter Power-Up Punch Mega Kangaskhan variants is weakened significantly. With how centralizing Mega Kangaskhan is, this is very, very important.
I probably don't need to do any more comparisons - the Mega Kangaskhan match-up speaks for itself.