Question

What is a good SP. Defence Wall?

Answer 1

Blissey.
THE best Special wall in the game.
Nothing can beat Blissey except, the only flaw for her is her terrible Defence.You may have to get a Bold Blissey, or invest quite a few amount of EVs for Blissey.
Blissey can be used as a Staller, and much more.
Check: > http://www.smogon.com/dp/pokemon/blissey

Answer 2

Umbreon is an excellent wall, for both physical and special defense, he has plenty of support, attacking, and status moves to keep himself safe from danger. Bronzong, metagross, and steelix are all good physical walls. Milotic and blissey make for good special defense walls as well.

Comments

I got Umbreon in my team as a Baton Passer already

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That's why I suggested more than one...