So it is all because The Coin can trigger "Combo" effects. It is actually completely overpowered. When a rouge is going second they can:
1. Coin -> Defias on turn 1 for 2 minions for a total of 4-3. All on turn 1.
2. Coin -> SI:7 on turn 2 to kill the opponents 3-2 and get a 3-3 out on the field.
I'm not going to go over every combo but these two are the ones that stood out to me the most. I'm sure there are others.
The reason why this is overpowered is simply because a rouge going first has to actually combo his cards out w/o the free combo coin gimick. That means with the same cards he can't Combo Defias on turn 1 or combo SI:7 on turn 2, not to mention it has to be played a whole turn later and w/o the combo effect.
I'm not saying the coin is OP. I'm saying The Coin shouldn't trigger combo, it's pretty unfair since the first player doesn't get a free card to activate combos.