Alright, first and foremost I want to congratulate you guys at OOO for somehow managing to make the Wildwoods difficult. I really like what you've done with the area, and how you somehow managed to make the Radiant Silvermail useful. Good job and such, and I'll elaborate more on it somewhere else. Summary, it's cool.

And now I will explain why you are all horrible people and I hate you.

Snarby is broken. Seriously. Completely. Broken.
Okay, so I get what you guys were going for difficulty-wise, and honestly, I like a lot of the ideas. Having Snarby actually attack you earlier in the level is a really neat concept, and the boss fight itself is also full of great ideas. Great ideas, but terrible execution.
So here's the thing: every element in the boss fight works against the player, and while they would be acceptable on their own, they compound on each other to create a fight that just isn't worth it. Two Snarbies wouldn't be too horrible, since it basically would just lengthen the battle. Likewise, the silkwings would be manageable with one Snarbolax, forcing the players to take every opportunity to damage Snarby or else watch as he regenerates most of his health. And this is where the problems come in...
If it was possible to focus on taking out a single Snarbolax first, it wouldn't be so bad. It isn't. The Snarby Twins are identical, so it isn't possible to focus one just one without either getting lucky or being observant to a point that is unreasonable to expect from the players. Furthermore, (and this is a problem with the regular Snarbolax as well) is that the bell just sometimes doesn't work. Even if Snarby is literally RIGHT ON TOP OF IT, if the planets are in an unfortunate alignment at that point in time he'll just shrug it off like it never happened. Let's also take into account that Snarby becomes invulnerable again not only after a set time, but a set amount of damage (or at least I'm guessing this, as that's what it always seemed like to me. You guys would know this better than I do, I could be totally off on this one.). This means you can do X damage to him when he's vulnerable. Then, the silkwings heal him for Y. If your X is less than their Y, you can't win. You lose. Pack your bags and head up to Haven. Now again, if you could focus on just one of them, and somehow stunlock him with the bell immediately after he regains his composure (assuming the bell decides to WORK, that is...), you could take him down. Unfortunately, the likelihood of this is about the same as me going down into the Clockworks and finding ten Love Puppies in a row. It just isn't going to happen. Its not really worth it to kill off the silkwings either, since they're just going to respawn anyway, they don't give you anything of value, and focusing on them means you aren't damaging Snarby. It's sort of like the Royal Jelly all over again, except much worse. Using poison on the Snarbies might make them more tolerable, but then again I think the poison ceases working when they go all invulnerable again, which is when the majority of the healing takes place anyway. Besides, it makes no sense to use poison on a POISON based monster.
So then, Snarby takes a certain amount of damage while he's vulnerable, becomes invulnerable, and if you don't stun him again RIGHT THEN he'll either go out of range, the bell won't work, he'll heal using the silkwings, or you'll accidentally start on the other Snarby without noticing. You make no progress, and even if you do, you have no visual indication that you are (i.e. the new Royal Jelly's crown deteriorating).

This isn't difficulty. This is tedium. And that's no good.

Look, you have a lot of interesting ideas for this guy, and I do really like those ideas, but you're really not making this guy any more difficult.
He's tedious. Everything about that fight is tedious. It's not something you can learn to deal with, it's not something that can be dealt with using skill (seeing as part of the fight rests on whether Snarby and the bell decide that you can hit him now). It's just tedious.
It probably isn't impossible, and I'm sure with enough messing around with things he could be taken down, but really, it's just not worth it. Even in this scenario, you're asking your players to adopt a single, concrete mechanism to deal with this thing, with any deviation resulting in the bosses healing and essentially restarting the fight, and even then this would probably take longer than Vanaduke could ever dream of.
Changes need to be made. Serious changes.

Okay. End rant. I'm done.

Again, level is cool, boss sucks slooms.