Mynd, Gwneud, Dod, and Cael all have irregular forms in their concise constructions. List below

Irregular Forms Table
Mynd (to go) Gwneud (to do, make) Dod (to come) Cael (to get)
Past Tense Concise
Fi Es i Gwnes i Des i Ces i
Ti Est ti Gwnest ti Dest ti Cest ti
Siân Aeth Siân Gwnaeth Siân Daeth Siân Cafodd Siân
Ni Aethon ni Gwnaethon ni Daethon ni Cawson ni
Chi Aethoch chi Gwnaethoch chi Daethoch chi Cawsoch chi
Nhw Aethon nhw Gwnaethon nhw Daethon nhw Cawson nhw
Future Tense Concise
Fi A(f) i (Gw)na(f) i Do(f) i Ca(f) i
Ti Ei di (Gw)nei di Dei di Cei di
Siân Eith Siân / Â Siân (Gw)neith Siân / (Gw)naiff Siân Daw Siân Ceith Siân
Ni Awn ni (Gw)nawn ni/newn ni Down ni Cawn ni
Chi Ewch chi (Gw)newch chi Dewch chi Cewch chi
Nhw Ân nhw (Gw)nân nhw Dôn nhw Cân nhw

Note that letters in brackets are added to make the verb formal. To not include them would mean the verb is said informally. Another way to make a negative verb is to put "Nid" before it, of which will require you to remove the "dim" that comes after the negative verb.

Note that when the verbs are negative, they undergo a soft mutation, excluding "cael" (to get), of which undergoes an aspirate mutation.

Note that when the verbs are asked as a question, they undergo a soft mutation.