Hee. Weiird card. I'm not sure it does quite what you were after, as I don't think this deals or receives combat damage. Is the intent something like ": Fortified land becomes a 0/6 creature. Activate this ability only if you're being attacked"?

What if could just block as though it were a creature? I was trying to avoid actually making it a creature, since I, personally, tend to find it weird that Walls are creatures.

I think we might as well make it a 0/6 creature. That, or give it an ability similar to Aurora Wall.

Yeah. This card is going to be setting a precedent. I don't think we want to tell people that this is how fortifications normally work...

I think this will actually work like Immovable Object, which isn't really what you want, most certainly not at common. Just let it turn the land into a 0/something creature. (I also think 0/6 is too big to have a common repeatedly generate. This would be plenty good enough if it made them 0/4.)

...Okay, I wrote the above assuming that the Fortify cost would be mana. Nonmana Fortify costs I think are also something we shouldn't have at common (cf Piston Sledge). It's less good now than I thought it was due to the implicit sorcery-speed of Fortify making it quite hard to find creatures to sac to this, but it's got a different reason to not be common.

I quite like the flavour "can block as though it were a creature". (I think I would not specify a P/T, but say "if it is dealt at least N damage, unnattach ~.) It sounds more like an actual fortification.

However, in Magic, walls are usually represented as wall creatures, so the simplest execution is probably "becomes a 0/4 creature", and then at least you use up your lands if you keep chump blocking.

I also like the "sacrificing slaves to build edifices" flavour. I'm still not sure we'll have enough ideas for fortifications to make them worthwhile, but I'd suggest trying out some of the common versions and see how they play.

Originally, the fortify cost was sacrifice a creature. I'm sure this is tied into black, and was for the same reasons why I made my Fortifications require some alternate form of payment, but if we're going to have one straight up man-land in common, we probably want it on the 0/6. Now it just feels like an 0/6 with ", Sacrifice a land: Regenerate this creature." which seems fine.

I'm also leaning on just making this a normal creature. I like the oddity that this card is, but that line of text looks like it belongs with Mono-White, not the 'breath of fresh air' normal creature that this slot desires. Any body want to defend the quasi-creatureness of this card slot?

Added to file.

No response, so I took the liberty to change it to a 0/6.

I think I must have missed your last update. I think if we're having anything vaguely manlandish on the common fortifications, it should be the simplest possible manland, which this comes close to. But I think 0/6 is too big, too fiddly to get past in Limited. I'd prefer 0/4 or 0/5.

0/5 it is. While I agree with your premise, making this a 0/4 is getting dangerously close to turning your lands into chump blockers. Chumping with lands is going to happen, but I don't want it to be a regular thing. I'd much prefer adding to the cost and activation than going that route.

It turns out that fortifications are good with all-in red. At first, I was swearing at myself for having fortified a land, then, next turn, top-decking a yeti. Then my opponent pointed out that I could just tap my land. Sweet!

Haha! Nice interactions like that between our disparate themes are very rewarding; all the more so when people not on the design team discover them :)