This is Pretty Serious Party By The Pool and Formula X TNT:
Actually I think the best combination I've come up with is this one, from somewhere over on the other side of the blue wheel, where I put it over a messed-up nail that was very dark blue. (Actually I think it was two different ones - it looks like I wrote Blackout and then scratched it out. I think when I went to put the second coat on I put Cynthia or something else on top of it by accident. And then, eventually, TNT on top of that.)
(Another layering note: I've tried Party By The Pool over several different blues at various times, but the best one I remember was one I tried on impulse - I put it over Zoya Liberty, the bright-blue texture, as a sort of a jelly sandwich. It looked really great that way.)
I'm pretty sure I saw PbtP on Pretty Serious' website fairly recently, but it doesn't seem to be there now. I think there were some re-released older polishes lately, so it may have been in that bunch. (I did find a blog entry about it, though. It was one of the first polishes of theirs I bought - and for that matter I think I bought it from Llarowe, not directly from them - and I didn't realize it was a Christmas polish til I saw that just now!) As for TNT, I bought it marked down, so I'm pretty sure that it's gone from Sephora's roster now.