Acid Rain

... won't be altered.

Why? Because it's so at odds with itself and so out-of-mechanics for blue that it has to be redesigned from the ground up. I'll offer an enchantment to take its place, but it's so different that I've crossed into the territory of just designing a new card.

First off, that art's all wrong (all respect to NeNe Thomas, of course). It's a blue card that's hating on Forests, but the picture is of a statue -- a human creation, and thus a little out of green's purview -- being etched away. It should show wilted forests retreating before poisoned rain, not a sad angel slowly melting. Second, the card's a sorcery with a big, one-time effect, but acid rain -- not the card, the phenomenon -- has many subtle, long-term effects (granted, effects like etching away angel statues). If the designers wanted this to depict rain that's actually acid -- as in concentrated sulfuric acid pouring from the heavens -- they'd have to show that with the art, and they'd probably have to add flavor text to drive home exactly what's happening. (They'd also have to explain how it's just killing trees and not goblins, elves, dragons, nantukos, kavus and Garruks the world over.)

Then there's the whole problem of blue destroying lands. It's funny how many of these old cards have blue doing ridiculous, color-shredding things like this; most of the other colors generally knew their place and stayed in it. (Generally. We'll see some real color-pie benders in this set; this is just the tip of the iceberg.)

This takes a page from Quicksilver Fountain, a card that's slightly bluer than an island but came too early to be as blue as a Sarcomite Myr. There's also slight precedence for blue to lock players out of colored mana; of the three cards that make lands tap for colorless, one's red, one's green and the most recent is blue. (Two are red if you count Chaos Moon, but no one counts Chaos Moon.) Of those three colors, blue has the strongest portfolio of changing land types (and, thus, denying owners access to colored mana).

In keeping with the original, this card only hits Forests. It also has a stronger flavor tie-in with acid rain; it's a slow, cumulative effect that will eventually choke out opposing green mages. The last clause -- the acid counter removal one -- is there partly to keep the board state clean and partly to ensure that no one gets locked out by multiple Acid Rains (either consecutive or concurrent ones). Unlike some cards -- looking at you, Sensei Golden-Tail -- the effect doesn't fundamentally change how the Forest works. If a player somehow gets acid counters on his or her Forests while an Acid Rain isn't in play, nothing happens; not only do I think that's a cleaner design, I think it's more intuitive. Generally speaking, cards shouldn't do things while they're not in play. I think that's a pretty basic (though not ironclad) rule.