Overview
How to almost surely survive the Nidd.
First, you need to win the level.
It works pretty well on all the maps, but in order to do this glitch, you have to first get to the winning screen.
Wait until the Nidhogg is just about to eat you
Wait until the nidhogg enters the screen…
Pause the game before it eats you
And most of the time, the nidhogg will fly off course. This does not always happen, but, well, it sometimes happens.
Disclaimer and misc notes
Note that this does not happen every time. It only happens about half the time.
Fun fact: If you evade the Nidhogg, it might fly back for you, in which case, just press Escape again. The little sea/pit that the Nidhogg usually flys over will be like an invisible wall, and you can walk on its bottom.