Which brings me to a great word for this week: noxious. Apart from having an x in it, which is always a good sign, noxious is commonly coupled with words like fumes, weeds, or gases. And small wonder since noxious means harmful or injurious to health or physical well-being. It also means morally harmful and corrupting, so you can use it as an adjective: My nemesis likes to engage in hatching noxious plans against me, but I outsmart and outmaneuver him every time.
Since noxious doesn't end in the dreaded "ly" I think it should be used with abandon. It seems like a perfect word for dastardly character.