Alright, I made a setup for this beast. It seems like Mamanbou is underrated around here... However, I'll explain why this pokemon is your best counter against physical attackers.
Mamanbou
HP 252/Defense 164/Special Defense 92
Spread really doesn't matter, but it's important to get at least HP EVs over 200.
Ability: Regeneration
Substitute/Submersion/Wish/Toxic
First of all, switch into a physical attacking pokemon (e.g. Metagross).
Second, make a substitute as soon as you switch in.
Third, use Submersion. This makes your opponent's typing into pure Water, messing up (most) physical attackers. This could eliminate STAB attacks. If the target has a Water typing, I suggest just skipping this part.
Now, finally, use Toxic. This could mess up a TON of pokemon if you manage to pull this off. Your opponent, for the most part, won't know what's coming until you pull it off. Submersion will make it so the target will definitely be poisoned. Imagine a Metagross being badly poisoned!
You can stall pretty hard, and if you're still in your substitute you can annoy the hell out of your opponent.
On paper, it seems horrible. You might think it's impossible. But trust me, people really think Mamanbou is a pushover or might underrate it's ability to ToxicStall.
If you get taunted, you can always use Regeneration to gain some fast HP.
Also, in this set, beware of Empoleon, your #1 counter. It's pretty deadly since you can't Submerge it, and you can't Toxic it. Grass Knot is a one hit KO.