The dd invaders at floor 31-40 had Wall of D. Well, at least the rock guy managed to use one of them on me. Totally didn't see that coming, but I still beat him. So watch out for their backrow.
I cannot say for sure, but sometimes they do. Probably when you are just climbing the tower for the first time they appear a lot. However, when re-playing the duels I didn't notice any increase appearance rate.
Anonymous
Lovely Aster
