They also have Xatu and Claydol, though those two won't be as scary. Lunatone is a non-issue, as both of my intended Pokemon for this battle will be completely immune to all of its moves.

Any advice on specific Routes for EV-Training my Cacturne? I'm going for a defensive-special set (Pin Missile and Spikes are physical, but Pin Missile doesn't need TOO much of a boost, and Spikes aren't affected by Attack anyway), so I'll want Special Attack, HP, and perhaps some Speed EVs to round Cacturne out.
Also, if I ever get White and White 2 and can manage it, I am TOTALLY getting a Cacturne with Water Absorb, it'd be great for a Doubles team I have in mind.

Are there three or four Pokemon in competitive Doubles teams?