Edited further the title to include Zocc, since he is one that has a similar skill, too.
IMHO, I don’t think there is a need to update the cards. Nothing is vague on any of those heroes skills. It’s simple, really. Those afflicted with the skills of Merlin, Zocc or Alfrike automatically cast Mindless Attack when their mana is full whereby an ally of the afflicted hero is damaged due to it, unless only the afflicted character is the only hero left, then the MA damages the target himself or herself. It is akin to other mana controllers such as Hansel or Gretel or Pixiie but instead of damaging allies, it only damages the target of any of the three aforementioned Grimforest heroes and leave the mana at 50% (while Merlin/Zocc/Alfrike target lost all mana since they automatically cast Mindless Attack).
I am not a native English speaker yet I’ve reread their skills several times and I find no fault in it. It is as clear as day. But that’s just my opinion.