Is the last ability enough of a drawback to justify 2 mana of any colour? Then again, unless you can add more mining counters, you can only dio that three times. Unlike the other mines, this doesn't destroy itself when it runs out of counters.

Most players don't have any particular colour available; see Quenchable Fire. "Any player may activate this ability" costs are pretty much always colourless, for this reason. If you made the cost rather than , it'd be good.

Made the change to for 3rd ability.

Hm. Actually, not sure what I was thinking: this is still unprintably good. As a turn 1 land, it'll give you three turns of crazy acceleration before anyone's in a position to pay . Perhaps ", Discard a card: Gain control..."?

I'm not sure what the card used to do, but in its current incarnation it seems alright. Personally, I strongly dislike Contested War Zone and I wouldn't play this or that, so I think giving it away is a good drawback.

I have no idea how powerful this is. I do want to point out that you can't target in a mana ability, so this should be "Choose an opponent. That player gains control of ~."

Hm. Since returning the land to you is a choice of the opponent's, this card is technically worse than a land that tapped for colorless and said "Sacrifice ~: Add two mana of any color to your mana pool." I know it doesn't feel that way, but it's true. You know... barring cards like Brand.

It's an Ancient Spring that comes into play untapped, adds colorless, but the 'sacrifice' gives you the two mana you want, and your opponent's ability to use the land becomes a very big drawback. Seems fine to me.

It would be a fun political card in multiplayer. Everyone pass the land around the table, except to that one guy; he knows what he did.