Can I not say "Yn yr noswaith/nos" instead of "gyda'r nos" isnt that "With the night"?
Yes, you can :) "gyda'r nos" is more poetic way and quite traditional, but no one would not understand you if you said
"Yn y (y because it comes before an n) noswaith dyn ni'n yfed gwin".
Yn y noswaith... This is still being marked incorrectly - should I report it?