I was thinking about Aetherborn Wisp.

What about to say:
"When a player discards a card from their deck, Aetherborn Wisp gains +1 base attack and +1 health."

That would be nice when opponent e.g. used Praxix ability or e. g. an Crystal Shards is in play ;-).
But then the rarity of the card should be probably changed, too?

What do you think?