"I'm more famous than you."
Translation:Dw i'n enwocach na chi.
'Mwy enwog' is a possible phrase here and would be heard in some dialects. Generally shorter adjectives tend to add an ending for the comparative (and superlative) while longer adjectives form the comparative with 'mwy' (more) and the superlative with 'mwyaf' (most).
eg hot/hotter/hottest = poeth/poethach/poethaf (note the 'f' in the superlative is generally not pronounced and is often left out)
handsome/more handsome/most handsome = golygus/mwy golygus/mwya golygus