Sort of a reverse Temporary Shelter

Seems a rather fiddly way of saying "only produces colourless if you played it this turn". How about an Azorius Guildgate with "when ~ ETBs, add to your mana pool"?

I wasn't sure how to word that ability properly. Also there's a feel-good aspect with entering the battlefield untapped, which is also relevant for anything that affects the mana production of lands.

why would i ever want it tapped? my choices are 1. tapped, or 2. can add

Yeah, I got to admit, I didn't get the feel-good aspect either. My response was pretty similar to amuseum's. Kind of similar to a creature that says "You may choose to have this creature enter the battlefield tapped. If you do not, it gains Haste."

There ARE a couple of fun tricks here. You might want tapped permanents - or you might have a druid hanging around to untap it to get the colour immediately.

Seems pretty edge-casey, when the simplified "~ produces only colourless mana the turn it ETBs" would do a similar thing.

Alright, Thanks Vitenka, I think your wording works.

I repeat, the only reason I had the weird wording is that I wasn't sure about the better wording.

Oh indeed, there are differences (e.g. with Amulet of Vigor). But are those differences significant enough to make it worth the extra confusion and complication? I say definitely not. (i.e. Your changed version is much better.)

The name sounds to me, by the way, not .

still needs a replacement clause: "produces colorless mana instead of any other type."

Dunno, you get dunes near the sea; so is plausible. And grassy is plains, more than forests, though I could see a stretch to depending on art.

There can most definitely be scrub ecosystem on coastal dunes, hence why I picked the name.

I think "dune" will evoke "beach" to some people and "desert" to others. When it's the part of the name that's trying to be the blue part, having an alternate meaning of "desert" is unfortunate.

But eh, it's a very minor point. The art would help.

I think part of the problem with the wording is that you might be focusing too hard on keeping the second line clean. Does this work better, or is this what you're trying to avoid?:

­: Add to your mana pool.
­: Add or to your mana pool. You may not activate this ability if Grassy Dunetop entered the battlefield this turn.

Oh, and for what it's worth, "Grassy Shoal" would mean the same thing. So wouldn't Barrier Beach (or, at least that's what the Cape Codders use when writing in their newspapers.) I like Grassy Dunetop, though. More evocative.

"Grassy Shoal" sounds to me like fish swimming along with grass growing out of their backs. Which should totally be a Magic card, but probably not a land.