So I totally lied to you, as it turned out I did have the debut appearance of the Brat Finks:

…which just goes to show the vast Mikester Comic Archives is even more vast than
I am aware of.
Also, just get a load of this guy:

You will never be this happy.
image from Fox and the Crow #94 (October-November 1965)
…the Brat Finks were already there, beating Stanley and said monster by one issue:

Okay, that panel actually is from #95, and not their first appearance, but I was collecting SAHM stories, not Brat Finks stories, so I don’t have #94 in the Vast Mikester Comic Archives.
…Mostly I’m just posting this here for the sheer 1960s-ness of the title “Brat Finks.” Also, for that one Brat Fink wielding the axe:

Out of context like that, we’re just one brief leap away from a funny animal EC horror comic.
Tales from the Habitrail, with your host The Old Hamster Wheel Keeper.
…Sorry, gang, I think Christmas is getting to me.
image from Fox and the Crow #95 (December 1965/January 1966)