water cards in elements dun really seem to be sliding towards
big damage, Acheron would feel weird if put into game with
the other water cards.
Actually, damage ramp is something of a core theme for water.
Steam Machine and Forest Spirit are not really pure water card so
they can exhibits something different from the normal water cards.
Shard of Patience is indeed a damage ramp,
but it increases damage + toughness while your creatures are not attacking.
Acheron seems like a fire card, keeps rushing to attacking and
increasing damage over time, not suggesting it to be a fire card,
just dun feel too exactly matched with the usual water cards.