I think that as far as villians go, Dennis from the Spongebob Squarepants Movie is one of the coolest. He is a "cool" evil, no evil rantings, just so tough he can grow a mustache at will. Do you think he should return in the Tv show in an episode or special seeking revenge or something?

I agree with you, Dennis is one of the greatest villains I've ever seen, I think he should return for revenge

I don't really think that, he's a one-time villian.