Call of Duty: Black Ops 3 Zombies (DLC #3 Descent) - Vaporeyezed Trophy / Achievement Guide - In Gorod Krovi, use the Gigant Beam to kill 20 Zombies in one activation. [Bronze]

First you must turn on the power. Just open the doors and go to the power switch (see video link below for a tutorial).
Now head to the Supply Depot area. It's only accessible after activating the power. There's a trap for 1500 points called "Gigant Eye Beam". With one activation of this trap you must kill 20 zombies. The trap stays active for 30 seconds.
You can do this as early as round 6 or 7. Just run around the room in big circles to lure in enough zombies. When you have 20+ running after you it's time to activate the trap. Hide behind the light beam and the zombies will walk right into it.
If you don't get it on the first try you can activate the trap again (one round cooldown time).

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