Have to say, Toxic Spikes support really does both help and hinder Keldeo. I run Custap lead Forry just so the one layer helps against the likes of Keldeo, Chandy, etc.
Keldeo is the special Terrakion, everything is basically 2hkoed by rain boosted specs hydro pump aside from Jellicent and max sp. def latias which we don't see.
Salamence seems to be Keldeo's partner in crime, especially choice scarf Moxiemence, which takes out most of Keldeo's checks (Jellicent, Latias, Celebi, Dnite (breaks the multiscale for Keldeo to clean up)) with an Outrage.
Scarfed Chandy also seems to be a reasonable partner, takes out Jellicent, Latias, Celebi, etc.
Ditto is a nice check to all sets without the Sub, as Secret Sword ignores the CM boosts to special defense (watch out for Chandy though!)
But yeah, is pretty strong, and like Terrakion's Band set 2hkos everything, including resists (aside from Jellicent, which Toxic Spikes/HP Ghost takes care of with substitute)
Also, maybe a sub + 3 attacks could be considered? Although it doesn't boost up with Calm Mind, it just hits hard off the bat with a LO Hydro Pump/Secret Sword/HP of some time based on the team's needs (probably outclassed, but still a possibility)