Use of 'y' between words

[Hendrik]

@iforwynnjenkins

Then I heard ‘Mae gyda fi rhywbeth y dweud’ - I have got something TO say.
‘TO’ is used in both but ‘y’ only in the latter.

In these instances it should be an i, not y:
Mae gyda fi rhywbeth i ddweud.

This usage of prepositions is a point of confusion that pops up from time to time, so instead of trying to reinvent the wheel, I’m linking to an older thread containg excellent explanations:

When to use and when not to use 'i ' as a preposition before a verbnoun

In the sentence "Would you be willing to bring something to drink with you?’ (ch. 10 level 2 N) ‘i’ is used before ‘yfed’. In the sentence “Would you be willing to wait for him?” the ‘i’ doesn’t appear before the verbnoun ‘aros’. I’m puzzled why it is used before one verbnoun and not the other. Is it just an optional thing?