I have a theory on what the title for Avengers 4 might be, it might be

Avengers Extinction

like how Ultron told the Avengers in Age of Ultron. Or it might be

Name: Slasher

Host: Alex Scott

Color: Purple and black

Story: When the symbiote Slasher came to earth he attached himself to a host named Alex Scott who is a young teenage man who is at his school is an outcast. When Slasher attaches himself to Alex and they began bonding over time, and they become anti-heroes and want to turn their home city to a safer place for other people. Because of Slasher bonding with Alex, Alex has been doing better in his life.

Abilities: He can run really fast, is immune to sound and heat, he can form blades around his arms, super strength. Can grow tentacles on his back and spider legs. Super healing.

Design: Finger claws, Two horns on the head. Slasher is thin