Rive has added the elastic curve as another interpolation method with v0.8.899. Elastic curves can be used to create spring animations with just two keyframes.

You can further customise the elastic curve with amplitude and period. Amplitude controls the intensity of the transformation, higher the number higher the intensity. Period is the distance between waveforms i.e. the number of bounce/back and forth, lower the number higher the number of bounces.

Below are some examples -