I re-watched "Whom Gods Destroy" again recently and have to call attention to the "Shakespeare" scene when Garth ("Lord
Garth!) tears Spock a new one by totally wiping the screen with Nimoy. Nimoy tries underplaying Ihnat's over-the-top take and it just doesn't work. Ihnat, and to a lesser extent, Yvonne Craig own this episode. I can count on one hand how many guest stars that can take a scene, let alone a an entire show from Shatner and Nimoy.
What's brilliant about Ihnat is that for the longest time he was a true acting "chameleon", always pulling me into a given performance and then only at the credits did I realize it was he I was watching! The Trek episode is one of his over-the-top performances (1968's Madigan
is the other) and The Mission: Impossible appearance is as subtle as can be. He appeared on M:I three times, but none more memorable as intelligence agent Stefan Miklos.