+16-18 stock (8-10 clear income) from a Nature isn't so drastic - Ancient Sage ans Deathwood Shaman do the same thing. But -16-18 stock to the opponent seems completely wrong. It's like very cheap rare Blizzard plus Ancient sage in one card. I guess it's even stronger than Corrupted woods used to be.
And don't forget that Nature rares are the easiest to summon.