We figured out the latest puzzle over in the DT Discord, so I'm going to post what we found here, so everyone's up to date.

Anyone who wants to remain unspoiled and solve it for themself before looking behind the curtain can find everything they need
here,
here,
here,
here, and
here.
Here's an in-studio image of Mike Mangini from the tweet in the third link. Read on past this image for the spoilers on the puzzle and how we solved it.
(Click the image for the full-size original)
So,
this Tweet contained some Webdings. The way to get those Webdings is to type "+ OR - X H F B H O" in that font.
This Tweet is of a shift key. At first, I thought this meant we had to take the Webdings and put them in lowercase, but in actuality, what it meant was that we were supposed to shift the letters.
This Tweet is a picture of Mike Mangini at his drums, but he has a piece of paper at the top of the drumkit.
Although the plus sign is written rather crudely, the paper says "+2731/-65".
Finally,
this Tweet is telling us "Is the END the beginning, or the beginning the end? Are you looking at the result or the ingredients?" So, essentially what we have is that we're working on a puzzle backwards. We're looking at some cipher text, and we have to figure out what process this underwent to reach that point, and reverse it.
Also of importance is the blog post that prompts for the password screen. Note that the url says "webdings-is-the-final-result-how-did-we-get-to-it-add-four-digits", and the headline is "Protected: Webdings is the final result. How did we get to it? Then: -2000."
So, basically what we had to do was take the letters from the Webdings, "+ OR - X H F B H O". + OR - is telling us what to do with it, essentially, based on what the Mangini image's paper says; it says +2731/-65. If we take what this is saying for each letter, and shift it that much(+2, +7, +3, +1, -6, -5), we get... Nonsense. Because we're working backwards. This hint tells us how we got where we are, so if we apply this in reverse(-2, -7, -3, -1, +6, +5), we get "V A C A N T".
VACANT is not the password. We have to add four digits, as the blog URL suggests, and use the blog headline to do so. And once again, we return to the Mangini image; 2731 - 65 = 2666. Take away 2000 from that, put it on the end of "Vacant", and we get Vacant666. That is the password.