This is so much better than Ancient Tomb, which is already crazily overpowered.

But now this is way worse than a Plains. Why would you play this, unless your set needs you to avoid having basic lands for some reason?

Here's an interesting idea: ", Pay 1 life: Add to your mana pool. You gain 1 life."

The funny thing is that there are decks that would pack 4x that card. Ajani's Pridemate and Well of Lost Dreams springs to mind. It's even balanced in and of the fact that you can't activate the ability when you're at 1 without losing.

Actually, I think you could. It's still a mana ability, so it doesn't use the stack, so SBAs aren't checked between activating it and it resolving.

Well then, Dude's example is broken, only being a drawback when you have out Platinum Angel out, and you're at 0. Also [all the other cards I did not mention].