Counter
Jellicent @ Leftovers
Ability: Water Absorb
EVs: 248 HP / 252 Def / 8 Spe
Bold Nature
- Will-O-Wisp
- Taunt
- Scald
- Recover
Ah, Jellicent, the forgotten jellyfish that was such a pain in gen V. Though the lack of rain offense makes Jellicent far less clutch than he used to be, he retains a niche usage as a ghost that can spinblock against Starmie and Excadrill, serves as a half-decent stallbreaker, and is a full stop against one of the most dangerous wallbreakers in OU, Specs Keldeo.
Since we're focusing on Keldeo here, let's start with the obvious: with immunity to three out of four moves on Specs Keldeo's set, the only thing that can even touch it is HP Flying, which does fuck-all as far as damage even on a physically defensive set (which is good, because heavy defensive investment is necessary if your goal is to spinblock against Excadrill):
252 SpA Choice Specs Keldeo Hidden Power Flying vs. 248 HP / 0 SpD Jellicent: 94-111 (23.3 - 27.5%) -- possible 5HKO after Leftovers recovery
Basically, Jellicent can switch in on Keldeo even with SR and three layers of Spikes up and still recover off any damage it takes from HP Flying. From there it can start spreading WoWs to cripple the opposing team or chip away with Scald.
Max defense investment because otherwise this thing can't actually do its job against Excadrill. You can move some EVs into Speed - 88 brings it up to 178, which speed creeps Tyranitar with 76 EVs, but no one plays that anymore, so I prefer the full defensive investment to always avoid the 2HKO from non-LO Excadrill. If you're not worried about stall, then drop Taunt for Shadow Ball, which deals 25.3-30% to Keldeo and lets you hit Starmie hard.