Risk you'll have to take?
I don't know, I'm still new to the game, but these cards look useless against certain opponents;
![](http://images2.wikia.nocookie.net/__cb20090802205755/elementsthegame/images/6/64/Discord.jpg)
almost useless against rainbow decks
![](http://images2.wikia.nocookie.net/__cb20090802233408/elementsthegame/images/5/52/EnchantArtifact.jpg)
useless against decks with no permanent control
![](http://images3.wikia.nocookie.net/__cb20101106180722/elementsthegame/images/2/22/Purify.png)
useless against decks with no way to poison you (when considering the shard of gratitude and other healers are much better substitutes)
![](http://images3.wikia.nocookie.net/__cb20090802213539/elementsthegame/images/7/76/Nightfall.jpg)
less useful against darkness and death decks
Anyways, use against the opponent is kind of just an extra, the real use would be using it on your own creatures.