Hi,
I found a bug. This happened many times, so I'm certain this is a bug.
You know how you can acivate an ability or try to use a card, but then you realize you wanted to do something else first? Then, you can click on "cancel" as long as you have not used the spell/ability.
When I click on Death Nymph to acivate its effect and click on cancel, the game treats it as if the ability was used. So, I basically lose out for nothing when I didn't use the effect. I am not sure if this is just Death Nymph or if it's the same for other nymphs.