Answer
Yes, Rhys Ifans did act in the Marvel Cinematic Universe. He portrayed the character of Lizard in the 2012 film "The Amazing Spider-Man", which is considered to be part of the MCU. In this movie, Dr. Curt Connors, played by Rhys Ifans, undergoes an experimental procedure using lizard DNA to regenerate his arm, resulting in his transformation into the reptilian supervillain, Lizard.