Negative jump
A Negative Jump is a jump done with enough negative speed that Mario ends up going down instead of up. When Mario Single Jumps or Double Jumps, his vertical speed is set to a constant plus his horizontal speed divided by 4. This means that if his horizontal speed is high and positive, he will jump very fast upwards, but if his horizontal speed is extremely negative, he will jump downwards with high negative vertical speed for 1 quarter frame before terminal velocity takes effect.
The negative horizontal speed required to make Mario's initial vertical speed from his jump be less than 0 is -168 units/sec for single jumps and -208 units/sec for double jumps.