|NOTE: Must be done in one level!|
This achievement can be easily obtained on Day 32. The trick is to use to execute the chainsaw execution move on the zombies. Now, this can prove to be a bit tricky. You will want to do a chainsaw execution on one or two zombies, then run away so the others follow you, then get a few seperated from the group, then rinse and repeat until your multiplier is at 100x.
Alternate Method #1: Once you reach Day 14, as the level only allows you to use a chainsaw, simply keep using for the chainsaw execution to build your multiplier. Watch out for Big Guys, as you can't break their grapple.
Alternate Method #2: This can be obtained in the first Day of the Hell mode, as a few members have said they have had up and around a 200x+ multiplier.