Sonic Underground ran from 1999-2004, but they made an episode called Sonic Tangled in 2014, it aired once, and never mentioned again. No videos, no info, nothing. Just the name and air date. Does anyone know anything about it? Or is it like A Day with Spongebob?
Sorry, but I have no idea what you're talking about and I don't think anyone else will.
I found tons of fanfiction things involving Sonic and the Disney movie Tangled, but nothing dealing with Sonic Underground or official material. There was a real episode of Underground called "Tangled Webs", but I don't think that's lost.
It also doesn't really make sense for a series that ended in 2004 to have new content be created for it 10 years later out of randomness.
So unless you were looking at fanfiction, confusing it with some other thing, or trying to create another ADWSS scenario (cause I'm just not sure why you would specifically point that out), this episode doesn't exist in official form.