Woolfolk and Plastino bring Mr.Mxyztplk back for another round of zaniness in Action 208 (Sept. 55).
The story introduces the notion that others can move from one dimension to another by saying their name backwards, as long as they are in Mr. Mxyztplk’s presence. In most stories, this will result in them heading to the 5th Dimension, but in this story, Lois Lane gets transported to the 8th Dimension.
The imp then spends the rest of the tale trying to get Superman to say his name backwards, while Superman outwits him, and eventually tricks him into doing it himself, which brings Lois back.
The appearance of Mr. Mxyztplk has begun to change as well, and in this story he has progressed towards his Silver Age look.