Latias@Leftovers
Timid Nature
160hp 96satk 252Spe
Dragon Pulse
Thunderbolt
Roost/Recover
Psych Up
This came to mind as a check to Mega Slowbro, more specifically, the CroBro set. What this lets me do is spam TBolt on it until it rests, then swipe its Calm Minds with Psych Up and keep going. I originally wanted to use Taunt on Latias, but it oddly enough seems to be the only poke in OU that doesn't get it (alongside Latios). Weirdly enough, I thought of Psych Up when looking through its movepool and was inspired by Regice (of all things) to use it in tandem with TBolt. For those who don't know, Special Defensive Regice used Psych Up in RSE to beat CroCune and other CM-spammers, and this does the same thing but trades raw bulk for speed, reliable recovery, and a better defensive typing (and a touch more power). I never used it a lot in the games I played, but it's nice to have in the back for Slowbro-M, Zard-Y, Keldeo, Lando-I (the latter two like Calm Minding out of nowhere and Psych Up trolls the hell out of them), and the occasional CroCune or even more occasional BP team (I used it once against BP and nearly laughed myself to death, mind that Psych Up ignores Sub and Magic Bounce).