>>2153834140 EVs MegaMence after DD outspeeds fully invested Mega-Sceptile with Timid nature. Also, 136 EVs MegaMence after DD outspeeds fully invested scarfed Landorus-T with boosting nature, but you'll hardly find the latter because it can balk a 252+ Stone Edge at full HP:
252+ Atk Landorus-T Stone Edge vs. 212 HP / 0 Def Salamence: 208-246 (54.1 - 64%) -- guaranteed 2HKO
252+ Atk Landorus-T Stone Edge vs. 212 HP / 0 Def Salamence on a critical hit: 312-368 (81.2 - 95.8%) -- guaranteed 2HKO
Whereas Salamence can still kill it:
252+ Atk Aerilate Salamence Return vs. 0 HP / 0 Def Landorus-T: 268-316 (84 - 99%) -- guaranteed 2HKO after Leftovers recovery
252+ Atk Aerilate Salamence Double-Edge vs. 0 HP / 0 Def Landorus-T: 313-370 (98.1 - 115.9%) -- 87.5% chance to OHKO
So how do you kill it?
1- Scarfed Greninja reaches 565 speed with boosting nature, EVs and scarf; 514 if not using a boosting nature. Protean Ice Beam will kill it, period. If you let him dance twice, then it's your goddamn fault;
2- Choice Band Weavile:
252+ Atk Choice Band Weavile Ice Shard vs. 212 HP / 0 Def Salamence: 328-388 (85.4 - 101%) -- 12.5% chance to OHKO
3- Choice Band Mamoswine:
252+ Atk Choice Band Mamoswine Ice Shard vs. 212 HP / 0 Def Salamence: 348-412 (90.6 - 107.2%) -- 50% chance to OHKO
That's that, basically. But, see, these are obvious as hell to the point you can smell it coming the second you see the Team Preview. It also means that players will adapt and carry Pokémons against them, and when you're dealing with choiced mons only, it is an easy task to outplay them. And when something centralizes the meta at that level, you just have to quickban it and send a big dick to Gamefreak, hoping they will understand for once what the fuck they are doing.