ABC’s Once Upon a Time celebrated 100 episodes on Saturday night with, among other things, a screening of the milestone hour aka Season 5’s winter premiere (airing Sunday, March 6).

TVLine was among those on hand for the VIP presentation. Knowing that spilling full-on spoilers “comes with a price,” here are some teases involving Emma, Regina, the Charmings and the other major characters arriving (or already residing) in the Underworld.

♦ The premiere kicks off with one of the series’ most powerful and emotional cold opens ever, doing justice to storylines past and present.

♦ The episode is a bit Regina-centric, from both her current-day conundrum in the Underworld (Mayor Cora lays out a rather grim ground rule) to flashbacks of one of her birthdays, where a surprising someone sets out to gift-wrap for the Evil Queen the only thing she desires.

♦ A case of mistaken identity leaves one of the heroes a bit flustered.

♦ Fitting for the milestone episode, a character whom we first met in the series pilot and who has not been seen in a while resurfaces when you last expect — to great comedic effect.

♦ Under the oversight of the Blind Witch, the menu at Underworld Granny’s now offers gingerbread… and children :-O

♦ A first meeting between two characters just may leave you a bit misty.

♦ Seeing the key to Room 8 tees up a sweet moment between Henry and Emma.

♦ Freshly deceased Hook has seen better days.

♦ “Chip” puts in an appearance, sparking a flashback to a “lost” scene between Rumple and Belle.

♦ By the end of the hour, one character will experience an extreme reversal of fortune.

♦ From the first moment Underworld’s pampered overlord is revealed, it’s clear that Ally McBeal alum Greg Germann is having a helluva good time playing Hades.

Want more scoop on Once, or for any other show? Email insideline@tvline.com and your question may be answered via Matt’s Inside Line.