Any attack by any Mechatar at any moment can be a critical.

Criticals are good in a battle . They are high damage and are based on luck although there are some factors(a blast weapon is less likely to score a critical than a storm attack ) Upgrades can also affect the possibility of a critical occuring. Some special objectives involve criticals. Some criticals will deal more damage than others because of standard damage. For example, a weapon with 38 normal damage won't be able to perform criticals as high as one with 70 for normal damage. No matter what happens, there will always be a time where you will not score a critical