I usually start my games by getting f*** you, and luckily there's usually just enough enemies to get the full power up before the first wizard spawns. The trick is to get three enemies following you and just making a good shot. Something that helps me round them up close enough to hit them all is to run between enemies that are farther apart. Hopefully that helps! Good luck in your demon killing

As RiccTheThicc mentioned, and in my experience, you can roughly get this before the first wizard spawns and definitely before the first boss. It just takes some practice. I find that, when running around, you can lure the initial waves of enemies into a sort of triangle shape and then blow them away at melee range at the last second before they knife you to get points towards it. I tend to just pick off any shield bearers that spawn so I can focus on getting this with the standard knife demons.

Cheers - I've cleared most of the first wave out to the boss with just the shotgun but for the love of god cannot run F You up. Wallie is so easy to do but F You seems so tricky to judge the line up (e.g took out the first 15 enemies in 5 shots and not one counted lol). Need some practice I think.