The Sinister Six was once going to be its own movie in the Andrew Garfield Spiderman Universe and was obviously scrapped for a great reason.

Now Spidermans whole story in the MCU has been building up to this teamup with clues in both Far From Home and Homecoming with Vulture, Scorpion, Mysterio and Dimitri in the MCU and well finally see the Sinister Six come to life in Spiderman 3

Sinister Six MCU Lineup

Octavius (Mark Hamil)

Scorpion (Michael Mando)

Vulture (Michael Keaton)

Mysterio (Gyllenhaal)

Chameleon (Numan Acar)

Rhino-Alexander- (Any wrestler)

Marvel is trying to do villians havent seen on movie screens before but Octavius and Rhino need to be in it because you can not have a Sinister Six without Octavius and there has been a trend with Marvel teams where theres always a strong guy in their team like Avengers have Hulk, Guardians have Groot, and Fantastic Four has Thing so it is important that Rhino becomes a part of this lineup. Chameleon is Spidermans first villian in the comics therefore, hes gonna be one of the first Sinister Six members along Vulture and Mysterio and Scorpion who were all seen already.

The reason Shocker and Prowler wont be in the Sinister Six is because they are more street level than the likes of Octavius, Rhino,Chameleon, Vulture, Scorpion and Mysterio. These villians are all Avengers level threats so theyll just wait until we finally see Miles.