Between the masses of the Jovian planets and the stars, a new population of exotic substellar-mass objects (SMOs) is now being discovered in profusion, that are challenging our notions of what a planet, brown dwarf, or star can be. I focus on some exotic and distinctive aspects of the compositions of SMO atmospheres. In particular, I review the formation of silicate, water, and ammonia clouds, the role of rainout in altering the abundance of the alkali metals, and the suppression by atomic potassium of the optical fluxes of a methane dwarf such as Gliese 229B. Furthermore, I discuss the order in which various molecular, atomic, and condensed species might dominate or influence SMO atmospheres, with an eye to anchoring new spectral classes from T
eff ~ 2000 K to ~ 100 K.