Mongor's eyebrows change from being the same colour as the rest of his face and being black, back and forth several times during the episode.
Mongor's power is related to the amount of fear his enemies have for him, so that the more they fear him the stronger he gets, and the less they fear him, the smaller he gets.
(After Panthro seals Mongor's tomb)
Lion-O: Coming back here must have been the bravest thing you've done.
Wilykit: Oh, not really, Lion-O. It's just...
Wilykat: That we were even more scared of your anger than we were of Mongor!
Lion-O: For Thundera, for Jaga, and for the ThunderCats! Strike down this power of fear!
Wilykat: Don't look at him, Lion-O!
Lion-O: No, Wilykat! I no longer fear his power! And without fear, he is nothing! Go back to your ruined temple and leave the Third Earth to live without fear!
Mongor: There is no one to help you!
Lion-O: Halls of Thundera! Help me now!
Lion-O: Who are you? What are you?
Mongor: I am the power of everything you fear. I am in everything you see! I am all around you! Above you! Beneath you! I am Mongor!!!
Mongor: Wherever fear is, Mongor grows more powerful!
Mongor: No creature, no structure, no Third Earthling will escape the wra-a-ath of Mongor! Mongor is supreme!
First Appearance: Mongor