How would I achieve a static effect like the one in the beginning of Umbrella vs FLLFFL (https://www.youtube.com/watch?v=Fe-IWFYd4Ps)

Make a movieclip, scribble in a whole bunch of nonsense, add a bunch of blur to it.

The rest of the effect is occasional deformations of everything else.
y'know, to give that unstable tape feed feeling.

Thank you!!! I was on the verge of purging an animation. With this I can finish within a week or less.

You can also shape tween a bunch of big particles instead to give kinda an eerie effect like the beginning of forsaken beard. Just a little extra tip.