Part of a cycle with Crumbling Belfry, Hidden Armory, Mystic Grove which I just added, and Vanishing Skyline which was previously added. Each one gives you a small benefit to play with, at the cost of watering down your colored mana. I had someone say to me that they needed to remember to count these as spells and not lands... but I'm not sure why. Unless you're really heavy on the double and triple costed mana, they still provide the correct color... kind of...

That Mystic Grove bugs me, though. It's such a clean idea, but it looks very messy on paper.

I'd certainly count this as a land. (And I probably wouldn't play it. Where I would play Hidden Armory if I had any ETB effects at all.)

Well, I guess if you intend to use their non-mana ability, then they're not going to be available to make mana. And the ones that react to stuff you pretty much want to keep up all the time. This... this I can't see myself using unless I've got a really strange deck. And why is sac in red, not black? Black got mill; blue got loot... You could twiddle those three round in colour easily?

True. I think I just wanted to see black get a bit more mill. It's supposed to have it secondarily, but it only gets to do it when Dimir comes to town, or if it's needed for a very black effect. I'm cool with those three as they are. I think it gives them a bit of off-beat character. Besides... black sacrifices creatures to pay the bills, but it isn't supposed to be allowed to sacrifice enchantments or artifacts.

I also know that the ability to just sacrifice your stuff is strong, but not a common thing to build around. The ability to, let's say, make Anihilate half as good, or shut off Capsize is hard to ignore, though. Oh, and Threaten. I suppose I shouldn't ignore the obvious.