Fake traps are to fool the opponent, or so they don't know where you put the real trap. If someone moves on the place you set the trap, they are killed. I usually teleport someone to where I set my trap.

It's like a land mine and you get Two of them to place at the Beginning of the game.
It's invisible and if they land on a square where you placed one, they'll be killed. You can't be killed by your own (you can go onto a square where you placed a mine and you'll be okay.)
But you can also FAKE placing a trap on a square. (As can your opponent).
The idea of placing a Fake trap though is more for when you're playing online or with a friend because when you place the fake trap, it simply makes the noise like you planted one but they can't see what button you pressed to see if you planted a real one or a fake one.
Hope that helps ; )

actually u can only plant 1 not 2.
well where i like to put it is under my champion to the left of my leader. this is cuz most the time the CPU will exchange one of their pieces with my grunt to where they have a bomb and boom boom we both dead. i just use the bomb as a counter strategy for when the CPU does pull that stuff. but if the CPU doesnt then ill just use it by exchanging my Champ with one of theirs and boom they have 1 less Champ and im in a big position to win the game. then ill end up teleporting their other champ to the bomb and boom no more champs. i like to use Kill on one of the CPU shifters first and wait till the CPU ressurrects it so then it cant bring back one of its champions.
so ya thats how i use the bomb...