I dig the rootsy guitars and the vocal is super well done. That stepwise chord progression back into the main riff is cool. I like this song a lot.
Challengewise: Did you modulate? I played a long on the guitar a couple of times and I can tell you move downward in subsequent sections but it doesn't feel like a modulation to me. At any rate, it definitely doesn't feel like it embraces the challenge as well as some of the other entries.

I really appreciate you changing up the genre again. I never pictured you doing a Black-Keys style stomper, but you pull it off well. The problem I have with this song is your implementation of the challenge. It's the middle four lines of each verse, right? You're playing that lick in C, then you play the same lick in G (four steps down), then back up to C, then onto the next section. But I don't think what you've done here is modulation; it's just a progression. I suppose repeating a phrase within the same tonal center but shifted down could be modulation in some contexts, but here these licks are functionally standing in for chords, and so this modulation is just building a bog-standard I-V-I chord progression. Later on in the song you have this downward pointing chromatic riff, which fulfills the "downward" part but again I don't think counts as "modulation" meaningfully. It's frustrating because I do want to be lienient to you for shaking up your style during a moment when you really needed to. But your genre shift doesn't appear to me to have been related to the challenge, and the "modulation" appears to have been implemented in a way that just happens to align with a typical pop music harmonic convention, which gives the impression that the challenge didn't constrain the song or push it in any direction it wouldn't have gone anyway. Okay, I'm gonna go tip a table over and hide behind it.

UH! I really like the way this switches out of the rock 'n' roll riff into the darker, fuzzier chorus / bridge sections and back again. It's in more of a classic-rock register than I tend to personally enjoy but it sounds great and the performances are really good, I think it's one of your best this Nur Ein. UH!