A few frame drops at the start, sorry about that.
To get the glitch, play as either Diddy or Donkey, hold left on the side of the screen until you fall to the bottom and then (you might need to wiggle left right a little) hold down+right then jump and you will clip under the level. A lot of black spots will clip you in-bounds and stuck. The way I stay under the long stretches is that I jump to the highest I can before, then at halfway I hold down+right and jump to give myself the smallest positive velocity.
Some rough timings have had this on par with my gold for the split; no TAS timing yet, though because TAS uses some tricks to gain speed by clipping, it may be technically slower (but on par in practice) this appears to be much easier than the current method of using Donkey and clipping into (not through) the ceiling to avoid the fish patterns.
