Yawn + Protect just to account for anything he might do (bar Substitute or Lum Berry, which I was praying he wouldn't bother with). If he brings a Fight Gem against my expectations and manages to live an Ice Beam, for example, I'm cooked regardless of my defensive investment unless I can Protect after a Yawn.
I had also considered an Endure + Custap Berry set so that I could fire off Ice Beam first thing no worries (thereby fixing the Substitute problem), but figured it was too risky as Protect is way too intuitive a move to just slap onto a set in this format.
EVs are super simple, max Defense to tank hits (including any +2 hits from a SD set) and max SpA with quiet nature for Ice Beam OHKOs if he didn't bring a sash/yache (50% chance if he uses 252 HP). Without +SpA, I can never OHKO that Lando spread. Relaxed would guarantee survival of unboosted Hammer Arm + Superpower, but even without Relaxed I have a good shot at surviving that, so I picked the OHKO chance because otherwise a gem set could wake up and KO me 33% of the time instead of just roughly 17% of the time.
I was super scared of Swagger shenanigans here, and almost considered Lum Berry for it. I decided against it and realized that if he's going to play that 50/50 game, I'll just let him gamble it.