A while ago I introduced a little minigame into my comic. It started when I did a week of filler strips featuring a character called Bummy. He's a little simply-drawn dude with a massive ass. It ran for a week and was completely pointless, and my friend (now co-writer) Keith hated it.
So I started drawing him into the background of the main strip from time to time to bug Keith just for fun.
And then at the start of the current act, I started drawing him into the background of every single comic.
Eventually someone spotted him and I revealed the game, and there was a little rush of comments activity where people went back through the comic looking for Bummy. It's become a really well-liked feature of the site. If there's a subtle Bummy (or more than one) in a strip, people like looking for him and being the first one to point him out.
I'm sure something like this has been done before, but it's a fun little extra feature that generates comments activity and encourages people to look at the artwork and go back through the archive.
Does anyone else have additional hooks, minigames or easter eggs hidden in their comics?