Celebi @ Leftovers
Ability: Natural Cure
EVs: 252 HP / 120 Def / 120 SpD / 16 Spe
Bold Nature
IVs: 0 Atk
- Giga Drain/Psychic
- Recover
- Baton Pass
- Nasty Plot/Thunder Wave
As others have mentioned this team lacks a good Keldeo switch in, it also has problems dealing with Mega Lopunny without resorting to Protect shenanigans or Potentially losing Lando to an Ice Punch(/Beam), Celebi deals with all these issues, absorbs status for the team and can even pass a Nasty Plot to Keldeo or M-Diancie if you get the opportunity, alternatively yellow magic is always nice, Giga Drain is the best option as it provides recovery and hits Ttar that could be switching in on you decently hard, but Psychic can also be ran if you want to hit Mega Lopunny harder or deal with Amoonguss better.
The EV spread avoids the 2HKO from Specs Keldeo's Icy Wind after rocks, Mega Lopunny's Return after rocks and has enough speed for Adamant Bisharp (alternatively more speed can be run for Jolly Bisharp, the defensive EVs can be placed elsewhere if desired)