Term for when a character unexpectedly and dramatically appears at key juncture (which they will help resolve)

The examples that gave rise to my question are from Stranger Things, so my explanation with sort of draw from that:

Several main characters are gathered together, it's a tense moment, possibly filled with danger but not necessarily immediate, and then suddenly another till now absent main character unexpectedly arrives, accompanied by appropriate music.

From ST one can think season 2 finale when Eleven shows up at the Byers house after being gone so long; or season 4 when she shows up in Max's dream world (only Max is there so deviates from my definition). We could even count Eleven's first appearance if we losen the definition a bit again. Inevitably the shot starts at the shoes and pans up to draw out the event (this isn't universal, but interesting to note).

I noticed many more instances like that in this show (and not always 11) so wondered if filmmakers have a term for such surprise entrances of a person who will tip the scales in whatever challenges are coming.

Thanks for any ideas! And hey, feel free to invent a term if there isn't one