Is this card really that good? A lot of posts talk about how good it is, but I just fail to see it. A major point seems to be that you can deny your opponent the draw for one turn. But used like that, it's worthless: For every nightmare you play to make your opponent miss a turn's draw, you have denied yourself a draw by drawing Nightmare instead of something else. You have just procrastrinated the game one turn. And why would you use Nightmare instead of Reverse Time for this anyway? At least Reverse Time kills a creature.
It might be used to slow down FGs, but it's no FG killer, and it's situational: The FG needs to have an almost empty hand for it to be effective, and if it's not completely empty, you have to get lucky so that the FG isn't able to play more that one card per turn. As soon as he does, the effect is gone. And it's slowing you down too.
Also, Nightmare does not give the opponent "creatures of your choice." It just gives him junk cards to discard. There is nothing forcing him to actually play this card. I just tried Nightmare in the trainer: The AI no longer plays nightmared card blindly, breaking any attempts to use Nighmtare like this. And ofc, in pvp it never worked.
The only way I can see this put to good use is against decks with Fractals.
Oh, and this is my first post