Three acceptable realizations of /r/
Until 1957, only two pronunciations were allowed: an alveolar trill [r] and an alveolar flap [ɾ]. After 1957, a uvular trill [ʀ] was also allowed. A voiced uvular fricative [ʁ], used extensively in contemporary Standard German, is not allowed. Therefore, rot ('red') can be pronounced [roːt], [ɾoːt] and [ʀoːt] but not [ʁoːt].
Rhoticism
The vocalized [ɐ̯] realization of /r/ found in German or Austrian Standard German corresponds to [r ~ ɾ ~ ʀ] in Bühnendeutsch so für 'for' is pronounced [fyːr ~ fyːɾ ~ fyːʀ] rather than [fyːɐ̯].
Whenever the sequence /ər/ is vocalized to [ɐ] in German or Austrian Standard German, Bühnendeutsch requires a sequence [ər ~ əɾ ~ əʀ] so besser 'better' is pronounced [ˈbɛsər ~ ˈbɛsəɾ ~ ˈbɛsəʀ] rather than [ˈbɛsɐ].
In contemporary Standard German, both of these features are found almost exclusively in Switzerland.
No schwa-elision
Contrary to Standard German, /ə/ cannot be elided before a sonorant consonant (making it syllabic) so Faden 'yarn' is pronounced [ˈfaːdən] rather than the standard [ˈfaːdn̩].
Fronting of word-final schwa
In loanwords from Latin and Ancient Greek, the word-final /ə/ is realized as a short, tense [e] so Psyche 'psyche' is pronounced [ˈpsyːçe] rather than the standard [ˈpsyːçə].
Syllable-final fortition
As in Standard German, syllable-final obstruents written with the letters used also for syllable-initial lenis sounds (⟨b, d, g⟩ etc.) are realized as fortis so Absicht 'intention' is pronounced [ˈʔapz̬ɪçt] (note the full voicing of /z/, which, in position immediately after a fortis, occurs in Bühnendeutsch: see below), but Bad 'bath' is pronounced [baːt].
The corresponding standard southern (Southern German, Austrian, Swiss) pronunciations contain lenis consonants in that position: [ˈab̥z̥ɪçt ~ ˈab̥sɪçt] and [b̥aːd̥], respectively.
Strong aspiration of /p, t, k/
The voiceless plosives /p, t, k/ are aspirated [pʰ, tʰ, kʰ] in the same environments as in Standard German but more strongly, especially to environments in which the Standard German plosives are aspirated moderately and weakly: in unstressed intervocalic and word-final positions. That can be transcribed in the IPA as [pʰʰ, tʰʰ, kʰʰ]. The voiceless affricates /p͡f, t͡s, t͡ʃ/ are unaspirated [p͡f˭, t͡s˭, t͡ʃ˭], as in Standard German.
Complete voicing of lenis obstruents
The lenis obstruents /b, d, ɡ, d͡ʒ, v, ð, ʝ, z, ʒ/[7] are fully voiced [b̬, d̬, ɡ̬, d̬͡ʒ̬, v̬, ð̬, ʝ̬, z̬, ʒ̬] after voiceless obstruents so abdanken 'to resign' is pronounced [ˈʔapd̬aŋkən]. That is in contrast with the Northern pronunciation, which requires the lenis sounds to be devoiced in that position: [ˈʔapd̥aŋkn̩]. Southern accents (Southern German, Austrian, Swiss) generally realize the lenis sounds as voiceless in most or all positions and do not feature syllable-final fortition: [ˈab̥d̥aŋkŋ̩].