The other day I was going through a stack of old Sega games and came across one that really stood out. The label only said "Tecmo Soft" and has a rabbit on it. The cartridge felt much heaver than normal ones I have bought in the past (when placed on a scale it weighs 3.6oz where a normal Genesis game weighs about 1.8oz). On the back it reads "Tecmo Super Bowl Prototype version 08-05-93, give an address and a name.
I took the game over to a friends house to give it a try. When I started it up it was Tecmo NBA basketball. Thinking that was odd I decided to open the cart up. Inside I found the reason for the extra weight. There are four Eprom chips not just one. Each is labeled something different. So this got me thinking there might be a way to boot to the other chips. I think this forum would be a good place to turn to, to see if anyone knows what this is or any tips. Here are pictures of it compared to a normal game.
Nice Find! Especially with the intact front label. Since the label on back identifys the game, doubtful there are other games on the prototype. Worth trying different button combos for maybe a hidden menu though.