The ~ideal Tsi vowel system~ vs Tsat

/i iː u uː/ <ị ịị ụ ụụ>
/ɪ ɪ̃ ɪː ɪ̃ː ʊ ʊ̃ ʊː ʊ̃ː/ <i į ii įį u ų uu ųų>
/e eː o oː/ <ẹ ẹẹ ọ ọọ>
/ə əː/ <ạ ạạ>
/ɛ ɛ̃ ɛː ɛ̃ː ɔ ɔ̃ ɔː ɔ̃ː/ <e ę ee ęę o ǫ oo ǫǫ>
/a aː ã ãː/ <a aa ą ąą>

Final long /aː/ merges with final long /ɛː/ and final long /ɪː/ with final long /i:/. On the other side of the vowel chart, final long /o: ɔː/ merge entirely to /u:/. Meanwhile, final nasal long vowels are shortened (but Tsi retains long final nasal vowels as a result of the later loss of final nasals; this is probably a chain shift):

ya-qquŋ [joq'ʊ̃ː]
k!ǫǫ [k!ǫ]
jòò /ɟù:/
šaa /ʃɛ:/

Short unstressed /a e ɛ/ merge to /ə/ and /o ɔ/ to /o/. Final unstressed short schwa is dropped (in the few derived words with this sound):

rlàŋŋạ ['rlàŋ(]
bek!ek [bək!ek]

The limited prefixial frontness-based vowel harmony observed in all western dialects of Tsi occurs in Tsat, too - the vowel /o/ shifts to /e/ before front vowels (including /a/) and vice versa. In Tsat however this is extended further because of the aforementioned shift, resulting in the alternation of /ə/ and /o/ in a series of prefixes (the harmony is also visible in some function words):

to-llà [təl'là]
aŋŋo [oŋ'ŋo]
ya-qquŋ [joq'ʊ̃ː]

Final nasals are lost, leaving behind nasalised long vowels. Final nasal long vowels are shortened in those words with no inherited final nasal consonant, but retained where they reflect the recent loss of a final nasal consonant:

ya-qquŋ [joq'ʊ̃ː]
k!ǫǫ [k!ǫ]

Consonants

[fʰ] mergest with inherited /w/: fháág [wáːk] 'older sister'

Final stops are devoiced: ktọp [ktop] 'pebble', ktọb [ktop] 'pure water'

Codaic /l lʰ/ are both labialised, producing diphthongs: ŋbą́lh [ŋbõũ] – dagger

Final nasals are lost, leaving behind long nasal vowels:

Final rhotics are debuccalised with lengthening: tbár [tbáːh]