So, after an excessive amount of lurking and playteasting with a friend of mine, my thoughts on the tier! (I love this tier too much to wait for Mambo's big changes xD)
Let's just get the obvious out of the way:
Simisear needs to be S+ now. Anything that can even hope to check it either takes heavy damage doing so or can't switch in on an attack / live the next one. I have found that Lampent completely checks standard Simisear sets right now, since I have not seen many Simisear running around with Knock Off (which smashes Lampent pretty hard), which is why I'm tempted to nom Lampent to go up to B, but idk if that one thing really deserves a rank-up. Sure, it's neat, but it's still kinda eh, espacially because Knock is still possible. If somebody'd like to talk that below me, feel free to, I'd love to hear some other player's thoughts.
Now, on to some other things that have been said above me:
I don't think Emolga needs to move anywhere, since nothing's really happened that helps it (if anything, the loss of Water-types to barely slap with Wild Charge hurt Emolga) and the most common Electric-type, buzz, commonly carries Hidden Power Ice which can 2HKO. Meanwhile, Emolga's strongest move against buzz is probably itemless Acrobatics, which deals less than 30% to standard Eviolite buzz. Plus, unless Emolga receives the Motor Drive boost, buzz outspeeds anyways. This is coming from a man who would love for Emolga to work, but it just doesn't. Cute, slightly niche garbage, but garbage nonetheless.
252 Atk Emolga Acrobatics (110 BP) vs. 0 HP / 0 Def Eviolite Electabuzz: 66-78 (24.3 - 28.7%) -- 98.4% chance to 4HKO
252 SpA Electabuzz Hidden Power Ice vs. 0 HP / 4 SpD Emolga: 158-188 (62.9 - 74.9%) -- guaranteed 2HKO
I'll agree with Rennyjesus on never really wanting Magmar over Simisear, since the only niche Magmar gets is the elemental punches, while Simisear gets Knock Off, Gunk Shot, etc., and that's only talking about physical moves. Meanwhile Simisear covers that specially with Hidden Power [insert type]. The drop in Speed kills Magmar specially as well, while being the bulkiest Fire-type in FU really means nothing with a) Stealth Rocks under every rug in the tier, b) a now-increasing preparedness for Fire-types, thanks to Simisear, and c) the fact that Fire is a garbage defensive typing anyway.
Not much to say about Delibird, other than I've never used it and never really wanted to either. Whirl is good right now, and outclasses it enough to keep Delibird where it is (although D-bond lead sounds kinda fun I guess I'll try it one day).
Masquerain is like C+ material at best, probably C or so. B- just seems way too high, Butterfree just outclasses it so much, even with Intimidate and Scald on Masq's side.
tldr;
Simisear to S+
Emolga & Delibird stay where they are at C
Magmar stays where it is at D
Masquerain to C probably / C+ at most
Discussion Points:
Lampent to B? bc it's a standard Simisear counter + Speedy w/ Choice Scarf who can hit fairly hard + less Water to stop it now