RESIDENT EVIL RESISTANCE

Put 8 creatures in 1 room. Then use any buff you have and shoot them and once all 8 are with the buff, cheevo will pop.

Not too difficult. When playing as Annette (1st Mastermind) when the survivors have to rush to the exit of the level in area 3. This will be your last stand to take down the survivors. Your Bio points will be heavily accelerated so you can spawn plenty of things in. Small or big, zombie dog x3, crawler, normal zombie, heavy zombie. Spawn it all in on top of each other. Make sure you have an Enhancer card in your inventory available. If you have any traps taking up slots try to get rid of them before you start this or as soon as you can during this to slow survivors down. Less chance of getting them again for a few cards. You can also use the card that makes you redraw a fresh batch of cards if you get it in your inventory and have no creatures. Once again after you have spawned all your creatures in. Make sure you use your Enhancer to buff them all. Achievement unlocks immediately.

I recommend using decks like this one I created. I called it Viral Insanity Annette Build where you can help slow down survivors as you go for this achievement.

You also can use it to get Powerbuff Girl achievement as well. This build is more meant for that achievement than this. The important thing is picking a room fast with lower Bio Energy cards.

Make sure you selected a handful of creature cards in your deck. You can use Enhancing Vapors for this too. Which is much easier, better than guns with similar effects.

Anything higher than 2 will take a little while or longer. I recommend choosing 0 to 2 cards. Trust me, especially late into a match they help out a lot.

You may also want to use Beastmaster to have a Zombie Dog spawn every 15 seconds while William is out. Also use what you can from the Mastermind's skills as well as equipment being Moderately or Greatly.

The achievement is having eight creatures with one enhancer used. Vapors covers more ground hitting more of them at a time. Plus, slightly uses lesser Bio Energy giving you more likely to use em.

I know this achievement can be very frustrating. I went out of my way to directly create a method that could work for you. If you message me, I'll tell you how to rebuild that deck.