I vote for Nidoqueen and NidoKing!
As for Ditto... It's hard to pull off it's main move to transform in the previous generations. But thanks to Imposer, this thing can be a threat.
One Ditto t rule them all
Nature: Any that raises speed. When you catch one, try to get one with high HP IVs.
EVs: 252 HP, 252 Spd, and 4 def
Item: Life Orb/Choice Scarf
Moves: ...Do I have to list them?
This little guy can wreck a team like Godzilla if the cards are played right. Choice Scarf is good for out-speeding the pokemon you are copying, but I feel iffy about using one... Life Orb is a good alternative.
Remember that you can't pass stat changes to Ditto because they are not applied to your foe unless it has already transformed.