The antonyms for the phrase "one level best" can be numerous, depending on the context. If we consider it regarding someone's performance, some antonyms can be average, below average, mediocre, or worst. If we take it in the sense of the quality of something, then some antonyms could be shoddy, defective, substandard, or inferior. Similarly, if we look at it from a motivational perspective, antonyms can include demotivated, poorly motivated, disinterested, or lethargic. In conclusion, the antonyms of "one level best" change depending on the scenario, but mostly, they indicate lower performance, quality, or motivation.