Yeah, I've seen people riff on xkcd comics before but they usually do a bad job of matching the handwriting/font (I don't know if Randall hand-letters these or if he types in a handwritey font). It's often a deliberately bad job, because indicating that they are changing the original is a part of the message/artistic expression. Like when a word is covered with a black bar with white letters in it in a different font, an obvious revision, it's like hearing a different voice interrupt.