The phrase "most mega" implies maximum size, power, or magnitude; antonyms would therefore be words indicating minimum or small size, weakness, or insignificance. Some possible antonyms for "most mega" could include "micro" (very small), "diminutive" (tiny), "weak" (lacking strength), "meaningless" (having no significance), or "insignificant" (unimportant). The opposite of "most mega" might also depend on the context in which it is used, such as in describing a specific object or experience, in which case words like "mild", "moderate", or "average" could also be considered antonyms.