A voiced epiglottal plosive may not be possible. When one becomes voiced intervocalically in Dahalo, for example, it becomes a tap.
Although traditionally placed in the fricative row of the IPA chart, ⟨ʢ⟩ is usually an approximant. The IPA symbol itself is ambiguous, but no language has a distinct fricative and approximant at this place of articulation. Sometimes the lowering diacritic is used to specify that the manner is approximant: ⟨ʢ̞⟩.
Epiglottal trills are quite common (for epiglottals, that is), but this can usually be considered a phonemic plosive or a fricative, with the trill being phonetic detail. The IPA has no symbol for this, though ⟨я⟩ is sometimes seen in the literature.
Epiglottals are not known from many languages. However, this may partially be an effect of the difficulty European language-speaking linguists have in recognizing them. On several occasions, when supposedly pharyngeal consonants were actually measured, they turned out to be epiglottals. This was the case for Dahalo, for example.