Nice work, thanks for the puzzle! Definitely a fun solve and my favourite of your puzzles so far. I really like 4A and 11A (although it’s a shame the drop device isn’t in a down clue) and you’ve got some fun and solvable anagrams in there. I’ve not heard of 9D or 2D (perhaps I need more skincare in my life!) and I’m not sure of 4D as fill, since the plural form is obviously the standard, but you could probably convince me it’s fine.
I’m not sure on “demoted” in that context in 6A, the cryptic grammar doesn’t really work. Maybe you could try [Damn! Country went after overthrown rat], or for a different surface [Damn! Country follows tsar without a bit of scepticism], perhaps.
I’m also not sold on “superb” being abbreviated to S (9D). I can’t find any source for that abbreviation, but happy to be proved wrong.
Thank you for the feedback and kind words, Super/Superb can be abbreviated to S because of Tier lists! An internet thing I guess but I think it's common enough to be used in cryptics :D
1A: I like this!
4A: Also nice.
6A: I think [demoted] can work, but only if you're talking about a letter within a word—for instance, where [dropped] is currently used in 11A. To say that [A follows B] (as JWords pointed out), you'd need [A is demoted beneath B] or something more specific.
7A: Cute.
8A: My only concern is this is the same mechanism as 7A, and the surface isn't quite as good. If we're talking about sudden movements, I'd much rather have this be something like [Drugs afflicted cornea after dropping ecstasy with sudden movements]. (Note that that's not a great surface either, but it's closer to a real-world situation/sentence.)
10A: Wonderful.
11A: Cryptic sense is fine; definition is sort of meaningless to me.
1D: Nice.
2D: I don't see how a skin-care product can be "stroppier" (or "violently" angrier), but maybe this is a use I just don't know.
3D: My least favorite clue, sorry. No idea what a lowercase "sam" is, nor what "hooped injured" is supposed to mean surface-wise. Best I can see is that you're trying to describe a clean Sam hula-hooping whilst injured?
4D: This is absurd enough to work for me; the idea of a pig slicer being in a group is funny.
5D: My favorite clue.
7D: My second favorite clue.
9D: Really nice if this is meant to describe a person who singed an otherwise superb pizza.