Togetic @ Eviolite
Ability: Serene Grace
Bold nature, 252 Sp. Def, 252 Def, 4 HP
Nasty Plot - Boosts special attack
Substitute - The great defenses here make substitute viable with Togetic.
Wish - For healing HP lost with substitute
Baton Pass - Hand off the boosts to a special sweeper and go wild.
I think Togetic is the best candidate in the game for baton passing a nasty plot. Not many Pokemon can learn both of these moves, and eviolite Togetic has the best bulk out of all of them (except maybe Mew), meaning it can stay alive longer and pass a decent substitute. If you time it right, you should be able to pass the Wish as well.