Solid summary there. “Overrun by the unrelenting dead” – hopefully not a prophesy of the current world.
Part 1 – Dawn of the Dead vibe, except with witch and wizard! I thought that bit near the start with the military falling back, the tide coming, the muggles still not going down without a fight was super evocative of zombie apocalypse fights. There’s a horde and Harry is lucky to be on the roof.
I also really enjoyed trying them trying the different spells on mangled arm security guy and naturally Hermione finds something that works, but it feels very much like something that would work for a zombie – restrain ‘em!
I’ve also always appreciated a good “disarming” gag!
A couple of broomsticks would presumably deal with that only-on-second-floor issue once the escalators are out, but if they don’t have them…
Naturally disappointed that Erecto is for the tent rather than a cock…. Ok, ok, one dick joke here. At least I didn’t mention tent pegging. Wait. Shit.
Any negatives… There’s a few typos I guess! Got ‘be’ for ‘before’ – with it being a while since you wrote it you might well spot ‘em reading through now.