Ah crap, I was just about to post that... I guess this is what happens when you forget to reserve things huh?
Well in any case here's another mon celesteela normally walls but all of a sudden can't.
Landorus-Therian (M) @ Flyinium Z / Earth plate / Life orb
Ability: Intimidate
Level: 50
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Earthquake
-
Gravity / Smack Down
- Fly / Rock slide/tomb / Stone edge / Substitute / filler
- Swords Dance
One would expect lando to be completely unable to do anything with its pesky flying typing taking away those earthquakes and its sheer bulk making basically any coverage move bounce off, until you reveal Gravity, and now all of a sudden your Earthquake is basically Thousand Arrows on steroids. Needless to say it does not end well for steela afterwards.
+2 252+ Atk Landorus-T Earthquake vs. 252 HP / 252+ Def Celesteela under Gravity: 288-338 (141.1 - 165.6%) -- guaranteed OHKO
-1 0 Atk Celesteela Heavy Slam (120 BP) vs. 0 HP / 0 Def Landorus-T: 51-60 (31 - 36.5%) -- 54.1% chance to 3HKO
As for the rest of the set, Smack down is an option if you don't want opposing landos to hit you with their earthquake, but isn't as useful against teams with 2 or more flying types or unexpected subseed steelas, while Z fly gives lando basically perfect coverage, annihilating the only ground resists left after Gravity/Smack Down in bug and grass types.