Just A Doodle

Quick doodle of ideas for villains and significant characters in a collage of disembodied heads. Not everyone is guarenteed, but I would love some input. Feel free to ask questions for elaboration.

From left to right, Mitsuru's teacher, (under) cold-blooded contractual killer with a cute and well-mannered disposition, (top) Mitsuru's antithesis with distinguishable skin graft from burns and multiple piercings, (hooded figure) masked assassin utilizing futuristic weaponry, and (far right) the main villain with relations to Mitsuru's teacher.

Commence judgement.