I just had a thought of a more automatic way to do something like this. You could have a bunch of nulls, tie them to each other via some sort of expressions with springy-ness, and then use them to define mask points.
Newton is a third-party solution for creating dynamics that would also do well at making the nulls move in a springy way.
As Rick and Szalam say - there is no 'easy button' for things like this. To keyframe it manually takes know-how, time and an understanding of the principles of animation.
One tip that might help is to draw your mask using Rotobezier curves - rather than conventional Bezier cuves with handles, and use the vertex tension control as you animate the points. Rotobezier will calculate the point (vertex) curvature automatically and will probably help you get a smoother curve and animation. Search the help for 'Rotobezier' to get started.
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Here's a quick and dirty example - to get the 'bounce' set a keyframe (kf) so your points overshoot the intended position, anther kf for the points undershooting the position and a final kf for the intended position- so the timeline looks something like this:

