Noooot suuure about this. The flavour is nice, minecart tunnels that lead you to new places; and tearing up land is the thing the city dwarves DO. (And the black dwarves, but they dig downward to demon doom land)

Probably too risky to give high end decks that kind of filtering, though.

It's an interesting mechanic. I think it's not really common, but apart from that it seems very nice: useful for deck thinning and colour fixing, but not actually mana acceleration so it's probably not overpowered.

the 5 lands made 'basic' - That's the 'one per booster' setting, right?

Yes. Except, heh, the way that Multiverse decides whether to use old-style or new-style booster collation is by whether the cardset has any mythic rares. It was with the introduction of mythics that they moved from 15 cards to 14 cards + 1 basic land (+ 1 token or tips-and-tricks card). So at the moment the Booster link will not include them in the basic slot. The Multiverse booster functionality was only ever going to be a rough approximation; the collation of Planar Chaos demonstrates that I'm not going to be able to create a sensible way for people to make any collation they want.

So at the moment "basic" means "won't show up in boosters at all". If you're adding mythics then yes, you'll get one per booster.

It'd be more normal to just let them be lands at common though. Most sets have one if not a cycle of common lands.

Well... drat.

Would need to change the flavour; but move this to green? That way white gets stuck with not having a mana land; which it cares about a bit less than other colours.

I think you said you wanted to make this tap as well.