MArcomage

It's a bit too strong for a common discarder and not too situational at all. Maybe have it replace a random (keywords u mention) card from opponent's hand?

Hmm, that could work. How about if it discards only cards of the keyword in question i.e. if Nature card is played, Nature cards are discarded?
Edited concept: Non-rares only.

With the new wording, what would you intend to happen if, for example, a card with both Nature and Restoration were played? Would it affect one of the keywords or both? There are enough cards that combine more than one of these that the effect should be clear.

Edited concept: "...those keyword(s)". If the played card has several keywords, I think this effect should apply to any number of them.

OK, but as it reads now, it sounds like if the opponent played Nature, it will discard all Restoration, even if that keyword wasn't on the previously played card. Is that intended, or do you only wish for it to affect those named keywords on the prior card?

Rephrasal is indeed needed. Working on it now.