"Hefin is faster than Dewi Lingo."
Translation:Mae Hefin yn gyflymach na Dewi Lingo.
'Cynt' is (apparently) another, irregular comparative form of 'cyflym'. Of course, it mutates after 'yn' as adjectives do.
Thanks very much, deeann333. All those languages you're doing must have you used to irregular forms. They throw me every time.