Titanfall 2 – Annihilation Trophy / Achievement Guide – Kill 25 infantry in 2 seconds as a Titan in the Campaign [Bronze / 15G]
Mission 9: The Fold Weapon
During this mission you will get a new Titan that comes with a minigun. It has an ability called “Smart Core” which automatically targets enemies. It also shows you the amount of enemies in the current area.
After fighting a bunch of Titans you will go through a tunnel with 30+ enemies. Wait for them to group up and then use the Smart Core. This should very easily get you 25+ kills in 2 seconds. Just stay at the opposite end of the tunnel so all enemies will be in your line of sight.
You can restart the checkpoint to try again.
NoUsableUsername says
I found it difficult to use the Smart Core personally, I used the Flame Core to get this achievement in the spot mentioned above. Just wait for the enemies all to appear and the flame core should kill them all instantly.