An "explosion behavior" is too vague a concept, and quite useless when there's a plugin like custom movement. Would the behavior be applied to the explosion object, or the sprites that are affected by the blast? This kind of thing is best implemented by hand. Objects that move with any kind of "physics" usually do so with custom movement or platform or physics some other behavior. It's best to come up with a simple formula to calculate the blast proximity and the effect it has on the x and y speed of objects. Custom movement makes this very easy to do so.
For physics, get the angle between the two objects for the movement vector, and use a formula which involves the distance between them to account for the closeness of the blast.