From the famous Simpsons/Family Guy-esque flash series 'College University' (aptly about a college), which in one episode you find out about an imaginary leprechaun named Studystlitskin, who appears when you study too hard. He can be a help, apparently, but also proves to most as a hassle and distraction from studying. The rules are: 1. Never accept his hard candy (which, if done, proceeds to be hit in the head with a mallet), 2. Never Chinese leg wrestle him, and 3. Don't make him think you have his gold. Studystlitskin is more of an antagonist, and thinks just about everything is his gold. The question one wonders if he really is imaginary, considering if he is 'imaginary', then why do all the college kids hallucinate the same leprechaun? Especially since most of them haven't heard about Studystiltskin until they meet him themselves.
CU Stu: Man... I was preparing for that crappy Econ. exam, and I got a visit from the study leprechaun...
CU Stu 2: Studystiltskin? Man that blows. Didn't eat his hard candy, did you?