Old Vauqun/Sound Changes

Old Vauqun is a direct descendant of Proto Vauqun-Adzovъd, and due to it's location at the easternmost extreme of PVA languages it earns the namesake of the proto language, along with its westernmost sister Proto Adzovъd. Note that IPA will be used for all transcriptions of the languages in question, regardless of the phonemicity of their standard writing systems.

Vauqun-Kfimea Dialectal
PVA maintained a distinct Vauqun dialect for some time before the split. Various isoglosses are shared with P Kf (esp. E Kf languages). These dialectal rules include:

I-Umlaut

[j] (in all positions) and [i] (when long or word final) trigger umlaut of preceding vowels, an intervening  blocks the effect from occurring [a o u ɨ] > [æ ø ʉ i]

Rounding of 
 * fɨrokje > firøkje
 * deðgajeːk > deðgæjeːk
 * suːrzi > sʉːrzi
 * vawojeːk > vawøjeːk (not *væwøjeːk)

[ɨ] and [ʉ] as manifestations of  alternated widely in PVA dialects; in the V-Kf dialect  was ʉ when followed by a velar or labial consonant (and when the product of an umlauted [u], as discussed above), otherwise it was realized as [ɨ] Realization of 
 *  = [gnʉːwo]
 * = [xrʉket]
 * = [venɨ]

 likewise had various phonetic realizations in the PVA dialect continuum, whereas in Adzovъd isoglosses it is almost unfailingly an alveolar trill, though in Vauqun-Kfimea dialects it also has a retroflex allophone (varying from [ɽ] to [ɻ]) whenever it is adjacent to a consonant (this likewise led to allophonic retroflexion of alveolar consonants. [t d s z n] > [ʈ ɖ ʂ ʐ ɳ] / _ɽ~ɻ OR ɽ~ɻ_. [x] and (from here on [ɽ] will be used in favor of [ɻ] for the sake of convenience, but the reader should not conclude that this indicates any preference for that realization of the phoneme.)
 *  = [reːɖɻu] or [reːɖɽu]

Palatalization of Velar Spirants

[x] [γ] (which might have had the allophones [ç] [ʝ] in palatal environments already) became [ʃ] and [ʒ] before [i iː e eː] and [j]. This became phonemic when various vowel shifts occurred later (after the era of PVA unity)
 * suxidvẽː (or perhaps [suçidvẽː]) > suʃidvẽː

Pre-OV
Palatalization of Stops

Dental and velar stops become affricates before front vowels and [j], and when after [j]: [t d k g] > [ts dz tʃ dʒ] / _[i e iː eː j] OR [j]_. [j] then typically disappears and causes gemination (whether it is before or after), unless certain lexical pressures keep it in place. The affricates that geminated underwent metathesis and lost their length (though this did occasionally fail to occur. Intervocalic Lenition of Nasal Consonants
 * sĩːkje > sĩːtʃːe > sĩːʃte
 * xrevde > xrevdze
 * totẽːk > totsẽːk
 * ajk > atʃː > ! atʃ (irregular, "correct" form [aʃt] unattested)

Nasal consonants lenit to glides or fricatives between vowels: [m n] > [ṽ j̃] / V_V Diphthongization of Nasal Vowels
 * ʂɽeme > ʂɽeṽe
 * venɨ > vej̃ɨ

Nasal vowels fracture into a vowel and nasal off-glide, the latter of which potentially assimilates into the following consonant (note that in PVA nasal vowels were never followed by nasal consonants or glides, also note that all geminates mentioned simplify when not followed by a vowel)

[ũː ẽː ĩː] > [øw̃ aj̃ ej̃]

[j̃ w̃] + [v b] > ṽː

[j̃w̃] + [d g] > [nː ŋː]
 * vẽː > vej̃


 * kɨnũːt > kɨnøw̃t

Deletion of Word Final Stops
 * dãːvo > daw̃vo > daṽːo
 * mĩːga > mej̃ga > meŋːa (contrast mĩːgeː > mej̃dʒeː > mendʒeː)

Title says it all :P [+stop] > ∅ / _ # Further Reduction of Dental Fricatives
 * totsej̃k > totsej̃
 * xʉrket > xʉrtʃet > xʉrtʃe

The dental fricatives

Early OV
Dephonologization of 

U-Umlaut

[w] [w̃] and [u(ː)] now trigger rounding of preceding vowels similar to the historical fronting effect of [j] and [i(ː)]: [w] and [w̃] cause the vowel in the syllable immediately previous to round, and [u(ː)] triggers the rounding of all vowels in a word when it appears word finally. An intervening [j] or [j̃] protects preceding vowels from a u-umlaut. ([a e i] > [ɔ ø y] /_(C)$...[w w̃] or /_...u(ː)#!_...[j j̃] Word Final Vowel Shifts
 * zaru > zɔru

(none of these shifts apply in monosyllabic words)

Short high vowels disappear word finally, and short mid-high vowels rise to take their place

[i u] > ∅ / _ #, [e o] > [i u] / _ #

Note that this causes a significant shift to the already rather impacted gender marking system for adjectives and pronouns. It also introduces word-final nasal stops
 * togru > togr
 * tɨbγe > tebʒe > tebʒi
 * tɨbγæ > tebγe > tebγi
 * eːkje > eːtʃːe > eːʃte > eːʃti
 * eːkjæ > eːtʃːæ > eːʃtæ > eːʃte > eːʃti (later > eːkki by analogy with words like tebʒi / tebγi)
 * keːro > tʃeːro > tʃeːru
 * ɶffu > ɔffu > ɔf
 * æffo > affo > affu
 * ræki > retʃi > retʃ
 * ʃnʉnu > ʃnunu > ʃnun