The antonyms for the phrase "most hundred-to-one" could be "least likely" or "unlikely." This phrase suggests that there is a very low probability of something happening, with odds of 100-to-1 against it. Therefore, the opposite of this would be something that is highly likely or probable, such as "certain" or "guaranteed." Other antonyms could include "common," "frequent," or "regular," which imply that something happens often or regularly. In contrast, "most hundred-to-one" suggests that something is highly unlikely, unique, or unusual. So, the antonyms would be words that convey the opposite meaning of rarity or improbability.