"Dewi Lingo is the wettest."
Translation:Dewi Lingo yw'r gwlypa.
I know it's a year later, but I think it's because you're repeating the "be-verb" here.
It was raining, of course, so they all got a bit wet. But then Dewi fell into the Taff....
Remember in Wales, it always rains, so when Dewi goes out with his friends there's a risk he could come back and be the wettest of the group, especially if he's forgotten his coat, as he tends to do.