In this tale that's composed just pre-war
A male sidekick's arose as of yore
With no Dwight Frye as Fritz
There's one right guy who fits
And it's Béla Lugosi's Ygor.
In Son of Frankenstein (1939), Béla Lugosi as Ygor replaced Dwight Frye, who was Fritz and Karl in the two previous Frankenstein films. I have a hunch this is the return of our feature, Dwight Frye-days.