Was the imposter Kane the undertaker or festus or both?

Luke Gallows. The Undertaker (Mark Calaway) dressed as Kane for one match only in the 90s when he feuded with Vince McMahon. He did NOT "play" Kane at all. He pretended to be Kane to get in the ring with Vince and unmasked himself and showed that he is The Undertaker there and then. Festus (Luke Gallows) played the masked Kane for the Kane Vs. Kane angle which WWE quickly dropped once they realised it was ridiculous!