Do you remember when you were in elementary school, and you sneaked a bunch of Monster In My Pockets in your backpack for recess? There, you could battle your monsters against everyone else's. Remember that? Nope. I don't, and I would be surprised if anyone really did, but that was sort of a thing for a while.
Decoys had a set of 50-100 figures, and they were received really well. Even today, people value Decoys on average a little more than your normal minifigure. I suppose the only drawback they would have in the eyes of your normal Transformer collector is that they did not transform. They were single mold rubber, and eternally locked in robot mode. Personally, I have no problem with that, but I'm a keshi collector.
On the back of all Decoys was a number. This number was to represent the strength of the robot, so when kids on the playground would reveal their single minifigure or their team, they could compare numbers to see who won. That's the idea, I suppose, but again, I never heard of anyone doing it.
Furthermore, Monster In My Pocket followed suit. They too put numbers on the back of their figures, hoping it would spawn a secondary need for their toys as game pieces, but at least in my childhood, I found it only created confusion. Was it a set number or the rarity? Growing up, we didn't really know, so it's really to no surprise, to my knowledge, the game ended there. Pretty funny to look back though.