Although I can't say for sure, I believe fairly strongly that another Dr. Blowhole episode, likely a special, will be coming in the future. Actually, I have believed this for quite a while, but only now have decided to comment on it.

My belief in such an episode is based on three points of evidence:

-- First, the United States Copyright Office's website has long listed two episodes whose titles reference Dr. Blowhole. The first, of course, is "Dr. Blowhole’s Revenge," identified by the production code 117. However, USCO also lists one simply titled "Dr. Blowhole" with the odd production code of 813. (No other episode production codes begin with any digit other than 1 or 2, except for an 815 without a full title.) This piece of information has been publicly accessible for months, so I'm a bit surprised no one picked up on it yet. (Though it's listed by USCO as a DVD, ignore it; nearly all other episodes are listed as such as well.)

-- Second, producer Bob Schooley referenced an (unspecified) upcoming special with a Twitter post (@Rschooley) on June 10: "Penguins at Comic-Con panel. Thursday July 21. 1:00pm. Sneaking songs from an upcoming special. Live!"

-- Third, Schooley, on June 24, posted a link to a photo of a computer screen on which Dr. Blowhole can be seen singing, captioned "Blowhole sings! See it at Comic-con." (I've uploaded it here under the title "Dr. Blowhole Sings.")

These three pieces of evidence, combined with my own gut feelings, give me reasonable (around 85 percent) confidence that another Dr. Blowhole episode will be in our future.