Ongoing observations in the strong-field regime are in optimal agreement with
general relativity, although current errors still leave room for small
deviations from Einstein's theory. Here we summarise our recent results on
superradiance of scalar and electromagnetic test fields in Kerr-like
spacetimes, focusing mainly on the Konoplya--Zhidenko metric. We observe that,
while for large deformations with respect to the Kerr case superradiance is
suppressed, it can be nonetheless enhanced for small deformations. We also
study the superradiant instability caused by massive scalar fields, and we
provide a first estimate of the effect of the deformation on the instability
timescale.
