Rather than make this ability tied to the land entering the battlefield, why not have it simply be a sacrifice ability on the land, like Horizon Canopy or Barbarian Ring? That way it works whether you draw this early and your Plains late or vice versa.

The old ability "Mana Flood" is now "Build." Instead of sacrificing the land when it gets played or having it come into play tapped, it now comes into pay tapped if you activate the build cost.

I anticipate that people will say this is too good to actually get printed, but I disagree. For one, it's not a plains so cards like Glacial Fortress can't interact with it and the build cost is grossly overpowered for its effect, which restricts it to emergencies as it's inefficient. I also just think lands in general need more TLC.

Yeah, Wizards' policy on "no card strictly better than a basic land" is one of those most frequently disagreed with by designers on this site (and elsewhere). I happen to agree strongly with Wizards' policy here, but you're free to disagree here :)

I think the change from sac to an ETB-triggered ability is quite reasonable.

If you make any land better than basic, all land is better than basic; and you then have to rebalance the whole game. (((Run and Hide))).

Still; I do miss the proper dual lands.

I'm not a fan of 'better than basic', but I'm won't argue with someone who disagrees with me on the subject. I will say, however, that not having a basic land type is probably more powerful than having a basic land type, sac lands not withstanding. Plains is probably the exception, since Plainswalking is very rare, and Cryoclasm hasn't been in the core set for a couple years.

What I really wanted to mention was that this card... it may or may not be able to tap for its own ability, and that's rather awkward. I assume you mean "As you play this land" instead of "When"... that solves some of the issues, since you can't activate it while the card is coming into play ("When" sets up a trigger you can respond to), and the land tapping in the process is a bit more intuitive. But even when fixed, I assume some players will try to tap it for its own ability anyway, because that's what players do... they try to look for an advantage, and if they don't know how something works, they assume that things work to their advantage. Maybe that's fine... the land taps itself, which should be a good hint... but it does make me wrinkle my nose.

@Vitenka. I think arguments can be made for this kind of "strictly better than basic lands." For one thing, you have to spend a lot more mana in green to tutor nonbasic lands like these than you would basic lands. And I disagree that it would unbalance the game because the majority of vintage and legacy decks I see hardly use basic land anyways, so why does standard have to be any different? It still irks me that Ruination never reached competitive status.

@Alex This card's ability is not an ETB trigger, it's a "cast" trigger like most of the eldrazi abilities. But since you can't cast a land, I said "play" since I figured that would be a distinct rule separate from ETB triggers that most other permanents have.

@jmgariepy So based on what I just said to Alex, no. You can't tap this land to pay for its Build cost since you have to pay for the ability before it hits the battlefield and then it enters the battlefield tapped. Even if you have an Amulet of Vigor you still can't use this land to pay for its Build cost because you payed for the ability before it entered the battlefield (unlike Rupture Spire). The fact that this is causing confusion shows that I need to change the way Build is worded. Let me think on it and I'll get back to you.

Sorry, that doesn't quite work within the rules. You can have Eldrazi-style "cast" triggers on any nonland card, but doing it on lands is much, much fiddlier.

For one thing, triggered abilities aren't "activated". For another thing, there aren't many sane modifications you can make to the act of playing a land. If your ability was written:

> When you play this land, you may pay . If you do,...

Then it'd be fine (although kinda odd-for-the-sake-of-it and should probably turn into an ETB trigger). But that's a triggered ability, which uses the stack; so it absolutely can be tapped to pay for its own ability.

If you want to modify the action of the land ETBing by being played, such that it'll enter tapped, you'll need to use a wording using "As" or "instead". Something like:

> Build - As ~ ETBs, you may pay . If you do, ~ ETBs tapped and you gain 4 life.

That works, for the same reason that Battlefield Forge (Edit: I mean Sacred Foundry) does. And you can't tap it for itself. That's using "Build" as an italicised ability word. Using it as a genuine keyword ability would be rather harder and even more fiddly.

Would this work? "If ~ would ETB, you may pay . If you do, ~ ETBs tapped instead and you gain 4 life." Sort of like Balduvian Outpost.

Edit: Oops, Balduvian Trading Post.

It would work in errata, but it's fiddly enough and "rules-ese" enough that I think it'd be unprintable on new cards.

Asking for mana costs in a replacement effect really doesn't work, and it's a subtle fact that no existing cards use such a template, because that requires a window for activating mana abilities, which can get really messy. To pick "Cards that Make You Want to Tear Your Hair Out for $400", suppose you have Opalescence Humility, and Ashnod's Altar against your opponent's Worms of the Earth. You play this land, tapping two Plains and sacrificing the animated Humility for mana, which was the only thing that shut off the ability of Worms of the Earth....EEP?

Alternatively, you could do like this:
": Put ~ from your hand into play tapped and gain 4 life. You can't play other lands this turn and you can't play this ability if you've played a land this turn."
Which is a bit messy, but... no... I apologize. "As" and "ETB tapped" is a much better alternative. I do find it annoying how a simple etb effect doesn't work well with untapped lands. It goes a long way to explain why they haven't done this yet. I assume we'll see this all in good time because it's good usable space, but it's probably been brought up in RnD twenty times and shot down twenty times for rules confusion/confusing players.

OK, I'm sorry the interesting variants earlier got whittled away, but I think the current version with the option to pay for an effect when the land enters is a good design: interesting, useful and simple[1].

I would still just have this come into play tapped (or produce colourless, or be legendary), to line it up with most current non-basic lands, but it's ok if someone doesn't want to use that rule in their sets.

FWIW, come to think of it, if the effect you wanted before was "You can either have this untapped, or have this tapped and pay 2WW to gain 4 life", would that be equivalent to just having it enter untapped, but adding to the activation cost?

[1] Edit: I think it's important that the effects are ones that give an incremental advantage at almost any time. Eg. gain life, damage to players, draw cards, etc. I think it would be a mistake to put too-reactive effects on the lands (eg. damage to creatures), because that makes too many feel-bad moments where you feel obliged to hold the land until later, which is interesting tactically, but probably putting too much emphasis on the lands for most players (and too non-interactive if they create board-altering effects that can't be countered).