Are there any consequences for the power being used?
Along with the villain aging in "relative time", the need for food and rest should make things more interesting.
Before the "Speed Force" was introduced in the DC's the Flash, the Flash had to consume lots of calories to maintain his speed.
So the energy to "freeze time", or "phase out of time" should have a cost to it. The longer one is out of the timeline, the greater the energy required.
In Star Trek: TNG, the episode "Force Of Nature", repeated use of Warp-drive in a weakened area of space, damages space/time continuum.
If the villain uses it over and over again in the same area, does it weaken space/time where it needs to heal before the power can be used there again?
Does one using this power leave a phantom echo in the area one moves thru? How about on the objects one effects?
In Star Trek: TOS, the episode "Wink Of An Eye", those living in the "rapid-moving" time, cellular damage means a very quick death.