Mew @ can't decide on item
Synchronize
252 HP/4 SpA/252 Spe
Timid
-Transform
-Psychic
-Aura Sphere
-Roost
Shuckle @ can't decide on item
Contrary
4 HP/252 Def/252/SpD
Bold
-Toxic
-Infestation
- Shell Smash
-Rest
Because Transform copies all stats besides HP, Mew transforming into Shuckle would become a Pokemon with ridiculous HP and both defenses, with THREE stats maxed. Toxic causes foes to take an increasing amount of damage each turn, and Infestation prevents those poisoned Pokemon from switching out. Shell Smash, with Contrary involved, would increase both defenses and protect it from setup. Rest heals all HP, Toxic, and forces the opponent to attack for 2 turns, wasting PP, while Shuckle does not. It seems to me like the ultimate stall.
By the way, should I give them Leftovers or Leppa Berries?