It wears yellow and has a small tank at it's back. Who is it?

Its gray and it has a chainsaw as it's right hand and it has no clothes who is it?

Its green and has black spots and it has claws who is it?

~Harder level~ It helps you but is soon infection who is it?

~Harder level~ It's not a bot but is lost who is it?

~Really hard level~Is a bot in plant who is it?

~Really hard level~ Wears yellow who is it?

~Easy~ Its the bot of metro who is it?