I like the card idea. Maybe change the topic of the thread to an actual card name though
I have also wanted a card like this and I'm sure someone else has suggested it before. I suggest it be called Immunity. I suppose there could be Temporary Immunity (cheap) and Permanent Immunity (expensive). It's pretty powerful to be immune to debuffs, but the trade-off is that it can be a waste of a card slot and gold use if your opponent never brought any debuffs in the first place. I like it.
Permanent immunity would be way too powerful
Let's leave the permanent immunity ability for the hero