Some isotopes of Uranium, plutonium, and other radioactive elements emit radioactive gasses such as Radon, Don't play with radioactivity unless you are fully trained in associated safety, handling, and storage techniques. We've mentioned ether and mercury in a previous mailing. Carbon disulphide and hydrogen sulphide emit dangerous fumes and are also quite explosive, steer clear. If you smoke don't do so when working with chloroform, this reagent is not inflammable but its vapour passing through the hot tip of a cigarette is converted to phosgene a good old military killer gas. Ammonia is yet another liquid that must be used in a fume hood, it has most unpleasant fumes.
Many acids including sulphuric, and nitric have corrosive fumes, yet again avoid inhalation.
Highly charged elemental masses , neither solid nor liquid, sort of like a cloud made of solids. As mentioned above I use gold plasmas with low charges in some of my work. A pretty cluey amateur in this area built a special magnetic retaining chamber in which he created a plasma ball using very high voltage. Idea was it would be held safely in the magnetic fields, supplying energy for his main project. Alas it was all too much for the fields and the thing broke down.