Clock Stopper Achievement in Final Fantasy XIII-2
Responded swiftly to the appearance of enemies.
How to unlock Clock Stopper
This achievement requires 100 consecutive preemptive strikes. You will know you got a preemptive strike right away if "Great!" flashes on the screen when you initiate battle. This will occur if you attack () while the Mog Clock is still in the green, or if it is yellow and you attack the enemy from behind.
This can be easily boosted easily by finding a non-aggresive enemy to strike (there are some in the very first area of the game), then once you've entered the battle, pause the game and select "Retry" - you'll be placed right outside the battle and can hit them again. Since you don't actually need to finish the battle for it to count, just repeat this quickly 100 times and you're done.
If you somehow make a mistake, you can reload a previous save without voiding the achievement, so it might be worthwhile saving every so often even if you're using the cheap "Retry" method.