All chainsaws all the time - and they don't run out of gas.  Definitely my favorite mutation so far. Played with some friends this afternoon and we had a blast.  You guys try this one yet?

I wonder if you can get that achievement using it.

Pretty fun though having AI makes things problematic (the AI will attack zombies that are attracted to pipe bombs, and will attempt to chainsaw a witch immediately after seeing it), and public dudes will often friendly fire you. Still pretty fun to me as long as I'm playing on Easy/Normal, though.
 
I'm more interested in that rumored "M60 with unlimited ammo" mutation.

@Mmmslash said:

" I wonder if you can get that achievement using it. "

I was actually just playing a little bit now, I like how it makes you stick together more but then smokers are just a bitch now.

Chainsaw Massacre  is one of my favorite mutations.  The entire game I couldn't stop smiling!!!
  
Yeah the Tank Burger achievement unlocks in this mode...however I played all six mutations and I didn't get the mutant overload achievement or garden gnome prop.  

" @Bigandtasty:  I was thinking more like the "Do an entire campaign, using only melee weapons" one. Confederacy of Crutches, I think?
 
This one. "

" @Bigandtasty:  I was thinking more like the "Do an entire campaign, using only melee weapons" one. Confederacy of Crutches, I think?
 
This one. "

Chainsaw Massacre is my favorite one so far. It's a ton a fun with friends and great for a lot of laughs. I only wish that it had Bleed Out's frequency of hordes. Still, it more than washes away the bad taste left by Last Man On Earth.

Oh god, that sounds crazy.