RESIDENT EVIL RESISTANCE

This guide is for those who have unlocked most or all of the mastermind's equipment chests and skill cards. This achievement of course is a lot easier to boost with a group of people, but in case you can't, this build was what worked best for me.

Mastermind:
Nicholai

Skills:
Ultimate Skill - Relentless
Passive Skill - Tracking Rounds Predator
Passive Skill - Firearm Efficiency

Radar Pulse
Reinforced Leghold Trap

Equipment:
1. Large Caliber Barrel II
2. Large Caliber Barrel III
3. Drum Magazine
4. Gyroscope

Deck:
Zombie
Land Mine
Tracker Mine
Leghold Trap
Rifle
Machine Gun
Immobilizing Rounds
Discount
Electromagnetic Shield
Converter Mod - Firearms

You want Equipment that will cause the most Firearm damage and you want low-cost skill cards so you can switch them out quickly to more favorable cards in your hand. Try lowering the survivors' health without killing them and immobilizing them before using the machine gun card. You must kill 2 survivors with 1 Firearms card.

It is easier when putting a leg trap on rooms or hallways. The way I did it was simply trying to lower their HP as much as I can when they are breaking the biocore. Saved my nade launcher and shot them. This causes 500 damage and both of them simply got defeated.

A good way to get this is assign the leg trap card befote survivors enter a room before a puzzle piece in the first area. If there are 2 weak people entering the room, gun the first 1 down with the machine gun card that gets stuck in the trap. Make the other survivor think you don't have the machine gun any longer and don't shoot for a while. When they try to get the 1st survivor up start gunning the other survivor. If they are weak they should go down. A great way to make this method a lot easier is to put perks on that do extra gun damage or extra clip length. These can be found in the customisation section. After assigning the machine gun you have 30 seconds to use it.