I don't remember very well how I got the herbicide, what I am sure of is that there is a command to invoke the herbicide item
The herbicide is used to unlock the entire farm, thanks to that you can kill the "immortal" roots
I doubt there will be a new mission, Chris's missions are supposed to end when you unlock his shop
They have added new enemies, in debug mode, in the character menu there are many skins of characters (about 100) and not characters (7), some I have not even managed to see, I think Chris is referring to the champions