For a solo Squigly, what is the best way to deal with a strong rushdown like Filia and extreme zone like Fukua or Peacock?
I played solo squigs for my first five months of playing the game.
In both matchups it's pretty unlikely you're going to be getting a charge, so dp is more or less out the window. Both characters have easy ways out of daisy pusher(filia updo and peacock L bang, i think fukua can dp super out of it).
For filia, do your best to keep her out and stuff her with j.hp and j.mp/j.lk. I usually tried to stay above her and catch her out with H Divekick if i thought she would stay in a dash for a bit too long or is going to press a button. You want to delay her getting close to you as long as possible, though depending on the circumstances that will be difficult and sometimes even impossible. Up close, you're just as screwed as anyone else unfortunately. PBGC Opera was generally how i found a lot of hits.
One thing that might help is that you can do j.lp (or j.lk at strange angles) into H divekick if you're fast enough, and each h divekick will net you a combo. Both are solid normals against filia, but I still find this matchup to be one of the most if not the most aggravating.
Peacock is a lot trickier, but I was able to find decent success with a tool that everybody often overlooks; level 1 sing. With peacock running all over the place and throwing things out constantly, catching her out with level 1 sing + opera has landed me countless combos on Beamsprout's peacock. The only thing to watch out for when doing this is that her airplane will home in on you and stop opera if it's already out, so you need to be extremely careful for that. Other than that, make sure you're mixing up your jump patterns and blocking for the majority of the time you're in the air. Only go for a divekick if you know you're going to be able to convert off of it, which means either a low M divekick or a (risky) h divekick. If you find a hole somewhere in their projectile pattern, try and work j.hp's in there somewhere since it can often catch them off guard and you can convert with an opera at some ranges. I've had luck with random silver chords but like any matchup, don't count on them.
The interesting thing about Solo Squigly is that playing it more or less forces you to block well, especially in matchups where you aren't going to be able to get a charge.