Celebi @ Distress Glass  
Ability: Natural Cure  
EVs: 252 SpA / 4 SpD / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Moonblast  
- Energy Ball  
- Nasty Plot  
- Earth Power

Celebi @ Groundium Z  
Ability: Natural Cure  
EVs: 252 SpA / 4 SpD / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Stealth Rock  
- Nasty Plot  
- Leaf Storm  
- Earth Power

Other Options: SubSeed (possibly done better by Shaymin), Swords Dance, Choice Scarf, Psychic, Synthesis, Time Warp is banned in OU