Power Mimicry is the ability to copy the powers and abilities of others through various mechanisms. The methods by which these are copied and any limitations - such as being restricted to only a certain kind of powers - vary depending on the character, but they generally need to see the power in action before they are able to copy it. Some characters can even apply this ability to martial and physical techniques, copying the fighting styles of others.
The user's copied abilities may be inferior to the original's, or may be retained only for a short period of time, but others can actually improve upon these powers. Others still actually steal the abilities that they copy, combining this power with Power Nullification; this is known as Power Absorption.
It would be a No Limits Fallacy to assume someone with this ability can copy anything used against them; even if they can copy the functions of the ability, they may not be able to copy its full destructive power.