My tactical take, don't know how many will find this interesting, but every now and then Pep amazes me.
1. Default Formation Set-Up
We setup in a 442 with Alvarez and Haaland up top with Foden and Bernardo on the wings. This is Pep's go to default formation even though most outlets will claim we play 433, we really don't. Pep also defends in a 442 block which he really likes as well.
2. The Press (which we didn't need much tbh)
From the 442 formation, Gundogan split the strikers and pressed in a 4312, Pep has also done this alot in the past, and it makes sense to have Gundogan do this and have Rodri stay back.
3. The Attacking transition (Forest pinned back)
This is the most interesting to me. The back 4 tilted left, to let Cancelo wide left and Bernie wide right. Foden drifts in the left half space, Alvarez just behind Haaland, Gundogan in the right half space, almost becoming like a 3151 in attack.
The middle 3 (Foden, Alvarez, Gundogan) was dangerous and the key was Alvarez imo, his goal was to be the free man.
If we build up on the left, it would be Cancelo-Foden, on the right it is Gundogan-Bernie. And since Haaland was occupying both Center backs, Alvarez' role was basically to become the free man on whichever side we built up on, and since he never stops running it was so effective in pulling Forest out of position to find spaces (Literally the goal in how Pep sets up his team to score goals).
Haaland was so effective in his few touches, but alot of space is afforded to him through a combination of his clever moment and in how we moved the ball around effectively like this, it's unstoppable, especially when the personnel are all on it.
4. The Backline
This is the perfect role for Walker, the inverted fullback position puts his weakness (on the ball) too exposed, in the back 3 he can just act an anchor to the midfield and stop counters.
Stones so much more comfortable in this game than others, remember he came back from an injury so not surprising that he needed time.
Dias was perfect, can't say much tbh, didn't put a foot wrong, I just think the other 2 needed more accolades.
5. The midfield
Rodri perfectly anchored Foden and Gundogan, and I think this is Forests biggest mistake, you CANNOT let us have free reign in finding Rodri, they could have caused more problems in there press but perhaps the 3151 caught them off guard.
Foden and Gundogan in the half spaces were deadly as there ball control meant our attack kept ticking and did not slow down.
Want to give special praise to Gundogan, while Foden was great, Gundogan clearly showed veterans experienced and even slotted in Rodri's role after he was subbed and perfectly understood how to manage it.
Cancelo and Bernie had the clear goal to basically be wingers and drive at them, they were very aggressive in this.
Gonna stop here, there is probably more that could be said, but those are my main points.