6-1 Any%
Warpless
There are two dangerous parts during this level: the middle of the first area, with the shield shyguys and pits, and the end of the level. A safer way to handle the first section is to tongue the spear shyguys instead of spitting enemies into them as shown in the video -- slower, but much safer.
The end of the level can be done as shown in the gif below, though newer players might want to flutter more.
Ending strats comparison: [1]