As for the entry itself, I actually provided four (arguing that since the Ring Cycle consists of four operas, there really ought to be four limericks, one for each). My entry, in case anyone is interested, is below. (I believe the one that was read on air differed slightly from this, since I mistakenly read from the previous-to-final version when I called the CBC's “phone in your limerick” line.)
The evil dwarf Alberich lusted;
The Rhinemaidens all were disgusted.
They treated him cold,
So he stole their gold.
Those Niebelungs just can't be trusted!
Then Siegmund runs off with his sister.
He said “I just couldn't resist her!”
Thought Wotan, “The lad
Is just like his dad:
My son is a champion tryster.”
Young Siegfried tastes blood of the dragon.
(Were it me, I think I'd be gaggin'!)
And at this point, you know,
There's still FOUR ACTS to go,
And my interest seems to be flaggin'.
Brünnhilde sets fire to the tinder,
And the son of Siegmund and Sieglinde
Leaves this earth as a roast
(Instead of compost),
And Valhalla turns into a cinder.