Considering the old film idea that it's difficult to make films with too many characters, just as it's difficult to juggle with too many balls, Spider-Man: Homecoming did particularly well to balance its cast. To that end, it shouldn't have been a surprise that its sequel should come with just as large a roster of key characters.
In the marketing, we were teased multiple villains, the possibility of other MCU characters appearing and the return of most of the principle cast from Homecoming, even with the Decimation having seen some of them graduated from school already. And even though some of them didn't quite come to fruition, this is a fairly stacked cast of characters.
That's not to say that they're all entirely great (nor necessary in some cases), so it's worthwhile ranking exactly where each character with at least some impact on the plot ranks...
WARNING: SPOILERS for Spider-Man: Far From Home follow...
17. The Seamstress
When word came out that Marvel and Sony were casting a mysterious femma fatale for Far From Home, everyone got quite excited at the prospect of someone like Black Cat turning up. Imagine all of our surprise, then, when it turned out that said character was in fact this weird Eastern European angry model.
As part of SHIELD's away team, she forces a child to strip off in front of her to give him the stealth Spider-Man suit in Prague, which is apparently all fine. Then she's used as an attempt to blackmail Peter by Brad, who wishes to manipulate MJ into necking on with him. It's all very strange and she's in it for about a minute, all told.