Irregular adjectives - Ansoddeiriau afreolaidd

da is an irregular adjective.   When using da in a superlative context, we use cystal. 

Irregular Adjectives

Absolute

Equative

as … as

Comparative

e.g. better

Superlative

e.g. best

da

cystal

gwell

gorau

drwg

cynddrwg

gwaeth

gwaethaf

mawr

cymaint

mwy

mwyaf

bach

cyn lleied / mor fach

llai

lleiaf

isel

mor isel

is

isaf

uchel

cyfuwch / mor uchel

uwch

uchaf