The first issue of Groo the Wanderer I ever read. The 4th panel contains a joke that sold me on the title. 

It’s a hidden joke as well. 

Groo the Wanderer was littered with recurring jokes, hidden messages and the like, and the “What manner of wizardry is this?” and “You fiend!” (with a wavey line beneath it) are carried over from a joke in the letters page. 

The writer, Mark Evanier, wrote the letters page as well, which was highly unusual in comic books. One day he received a witty letter from a fan that informed him that Groo could not be considered a true barbarian (in the Conan form) unless the character had uttered the words “What manner of wizardry is this?” by issue X, or alternately, the words “You fiend!” with a wavey line beneath by issue Y.

Evanier dismissed this in the letters column as ridiculous, then wrote the words into the same issue. 

Which you wouldn’t pick up on unless you read the letters page, at the back of the book, and then re-read the issue. 

So, basically, the fact that the writer took the time to include the phrases within the issue, and thus delight a fan who took the time to write into a comic book, made me think “this is cool, and how it should be”.