Hi. I'm still doing that Innistrad MtG mod for LotR LCG I mentioned long ago. And while doing it, I met an interesting dilemma.
Now, before I continue, I want you to know that I consider any kind of additional (printed) random on cards in competitive card games like Thrones or Netrunner a cancer, and absolutely despise it in any form.
But co-op is a whole another realm, and one with lots of possibilities. So I wanna ask - would you actually prefer or scorn printed random effects in a co-op card game? On player cards? On encounter cards.
To provide an example, I'll give you a weapon that in original MtG transforms into the demon once the weilder damages the opposing player. In co-op realm, however, I decided to make it a very powerful weapon which harms owner every time it is used. Here is a non-RNG version:

It provides stable cost to each attack within your choice of a card being discarded each strike.
And here is a RNG variant:

It boasts bigger attack value, but every card you discard is random and there is a chance that you'll accidentely lose this weapon and summon a powerful demon to prey on you, making using this weapon a dance with the Devil it's supposed to be.
So, what do you think on the whole topic?