I recall a story from Saudi Arabia. A reformist Imam was invited to a traditional Imam’s house. When he arrived the traditional Imam shot him dead. This was ruled legal because Islam can not be reformed. The penalty for doing so is death. It can be administered by anyone who feels he is righteous and correct in his beliefs. (In practice, to get away with this you have to have more followers than the other guy and they have to be more militant. However, if it’s not Imam to Imam any Muslim can kill any nonMuslim for a variety of reasons and this too is “legal” per Sharia.)
An example of Sharia law in practice is honor killings.