Hmmm, you might want to go for Nattorei/Ferrothorn;it has a weakness to Fighting-Type moves, but its defenses are so ridiculously high that they shouldn't be too much of a problem. Um, but avoid Fire-Type moves and, especially, Speed Boost Blaziken like the plague. Its pre-evolution, Ferroseed, is actually pretty easy to come by;just look around in Chargestone Cave.
Ferrothorn has a base Defense of 131, a base Special Defense of 116, a good Attack of 94, but don't expect it to outspeed anything. Since it's so slow, actually, you'd want to give it Gyro Ball, which it learns naturally, anyway. Also consider giving it Power Whip for some nice dual STAB.
It you want it to set up hazards, breed a female Ferroseed with a male Cacnea/Cacturne(for Spikes) or breed a female Ferroseed with a male Roggenrola(for Stealth Rock).
If you want it to be really annoying and wall everything that looks at it funny, get a hold of a male Cottonee and breed it with your female Ferroseed for Leech Seed.
Iron Barbs is a great ability(it's like Rough Skin), which is good because I don't think Ferroseed gets a Dream World ability....
As for natures, run a speed reducing one so that Gyro Ball is always at its strongest. Brave, Relaxed, or Sassy are good choices.
If you decide to go with Ferrothorn, I might suggest putting a Jellicent in there someplace;the two cover each others' weaknesses quite well.
*Takes a deep breath* X_x
Well, a time-traveling phone booth can only take you so far...