might not be possible due to the coding of the game
It could always be changed to make them discard their top card.
Trying to keep track of which card is responsible for a given death effect may not be feasible.
For instance, consider the poison mechanic. In order to know whether or not an opponent's card was responsible, you would have to track who owns each poison status that gets played.
This is important, otherwise the player could just start poisoning his own creatures to make the opponent discard.
AND, even if you could do that, how would you decide if it was the opponent's poison that is responsible and not a poison counter applied by this card's owner?
I do like the concept, but it will be a pretty severe anti-CC effect. Even if it doesn't stack it might be a bit OP. Especially since it is quite one sided... Remember that since creatures are currently the primary damage source in 90% of all decks, CC likewise plays a MAJOR role in the metagame. A card like this could potentially cripple direct CC in a one-sided manor.
And of course, there are still the difficulties in implementation I mentioned above.
What if it always made the enemy of a killed creature's owner discard instead?
Another option would be to have the effect only trigger on the enemy's turn.
This would be very interesting since it would leave poison (death's favored CC) as a viable form. Shields (which are an integral defense mechanism) would also remain viable.
In either case, there would no longer be a need for accounting of what card's effect lead to a specific death effect. This would GREATLY simplify potential coding / implementation issues.
