There is
an SDA thread for this game, and the strategies posted there for an any% run look nice and fast. (They're talking about the PS2 version, but every version's the same.)
I've found a small Mermalair shortcut, but I'll keep it to myself for now. I also plan to utilize
this glitch in Jellyfish Fields, found by Darxae on YouTube.
And
this glitch may be helpful if it can be done inside the "square" that the boss stays in. If it could be done, then it might save a few seconds.
I haven't been able to do jlun2's final boss glitch yet, but if I can't recreate it, we could always do something like
this. But maybe that's not very entertaining. The fish announcer saying the same thing over and over is funny at first, but gets kind of annoying near the end.
I'll have more time to work on this TAS in about a week. I haven't even had time to test which method of movement is fastest (jumping/double-jumping/walking) or run any levels.