Mega salamence really isn't that big of a deal if you run a 252hp, 252Defense Impish(+Def-Sp.A) Mandibuzz on your team. It's bulky enough to take some hits from its return. But Foul Play is really what takes it down. Even if it sets up one dragon dance, Mandibuzz can kill it with foul play and still live. Not to mention greninja is still more great than ever with the new meta. Basically any strong physical dragon or ice sp.A user such as garchomp and greninja with a focus sash can live its attack and 1 hit KO it via (dragon claw and Ice beam). But Mandibuzz is your best choice with Roost and foul play