@Beau Skunky  

 
Well I did say one of, not the most, Smooze is most definitely bigger (not even a question, that thing is the biggest creature in all of MLP, even the Ursa Major and Tirek at his biggest in FiM don’t compare to the OG Smooze which drowned all of Grundle Land and was even consuming Dream Valley and dwarfing mountains in some shots from afar) while Crunch and Squirk seem to be pretty even in most scenes, though when you compare Crank (who is bigger than a pony when he first appears) to him in most shots, Squirk does seem to be portrayed as bigger.
 
I could also include that green dragon monster who escaped from that fantasy land or Ahgg but I wouldn’t call them villains per sé, or at least not major ones like Squirk. The former didn’t want to be a villain but his job was to be the antagonist of the stories and Ahgg is more like a dog that is being ordered to attack.

@DarkCarioca  
What about Crunch, or the Smooze?

When you really think about it, Squirk was easily one of the most massive G1 villains.

He likes pony toys?