Sixty Second Shooter Prime - Chronomancer Achievement Guide
In order to start a Chain Reaction you will need to play a little bit to unlock the ability. It is also advised to wait until you unlock missiles before trying for this because it is the best way to trigger the reaction.
Any level 7 or beyond is fine to start the reaction in any game mode. When you are surrounded by a bunch of enemies simply pull the Right Trigger to fire the missile, starting the reaction or get you close to the 50 kill combo needed. Look for a red enemy and fire at him and kite him around the map. Your base shots won't damage him and will keep the chain reaction going for 15 seconds. I used the timer across the top to monitor the time. The timer is slowed down as is the motion in the game so in actuality you are in chain reaction longer than 15 seconds real time. The achievement will pop after the round is completed.
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