Recorded with an emulator and yes, I own the console and the game. This is from the "Incredible Hulk" game for the SEGA Genesis/Mega Drive. The boss is The Leader (The big brain guy). He doesn't do any damage to you whatsoever. All you have to do to kill him is an uppercutt. The thing lying in the ground is a pick-up that can heal the Hulk's health and make him super strong. I don't even know why is that thing there, it's not necessary. I challenge anyone to find an easier boss than this one ;)
NEW EDIT: 900,000 views!?!? HOLY S***!!! Now that's awesome, thanks alot guys ;)
NEW EDIT 2: HURRAY, WE REACHED 1,000,000 VIEWS!!! I'M SO HAPPY! THANK YOU SO MUCH GUYS =D
One thing that's been bothering me is that people are always referencing Bob the Killer Goldfish. Just think about that "boss" for a second. He doesn't have any kind of HP, you are not allowed to control yourself and, most importantly, YOU CAN'T EVEN KILL HIM! THE GAME DOES IT FOR YOU!!! That's why I don't consider that fish a boss. The minumum requirements for an enemy to be considered a boss is to get to control yourself and get actually a chance to kill it...
But hey this is my opinion of course, you have yours. I'm just glad this video brought so many responses and other "easiest bosses" videos here on youtube. It's actually popular :D