discarding invalid cards

[Boaz Reinders]

hey guys, I searched all over the forum but couldnt find a good answer for my question.

1 What If a player plays a card or a power wich at that time isn't possible?
for instance: throwing a potion against somewone with the rain coat.

2 What if a player discard a card to use an ability or power like theft ability on someone with the helmet of Peripheral vision.

Can the player take the cards back to his hand/in play or was it a dumb move to do and does he need to be punished for his stupidity (as in, he played the cards so he lost them to the discardpile).