Personally, I don't have a problem with counters that have abilities. After all, that's what +1/+1 and -1/-1 counters are technically doing. I can think of a number of designs where things got awkward because I couldn't give abilities to the counter itself... I just assume Wizards will eventually end up doing this at some point so they can keep moving forward (and a number of people have played with 'gold counters' in the past that you sacrifice to add one mana. This isn't that far away from that.)

The rules have to be written in the CR one way or another, if I don't want them written out on the cards (except in reminder text). I don't know if counters can even have abilities? I guess tokens and emblems (and other things that aren't represented by cards) can have abilities, so maybe it's possible... But that seems weird and self-referential to me, and I think it's cleaner to just make it part of the definition of what these counters are. Spending them for mana is just...a thing players can do, like playing a land.

Whuh? Why not make it a mana ability? Trying to write new Comp Rules to allow it to work "very similarly to a mana ability" sounds like a recipe for loopholes.

There was an issue with fiddliness here too, but playtesters pretty universally said it was worth it because the cards were good. Should definitely be kept out of common, though.

An intriguing idea to move this cycle up to rare, where it could replace the admittedly unprintable lands that are there now.

The "remove two thauma counters to add to your mana pool" rule would be a CR rule, rather than being written out on the cards, for exactly the reason Alex describes. I plan to have spells that add thauma counters to permanents (I just haven't put any in the set yet). Plus, the current wording allows you to remove one counter from each of two permanents to gain your mana, whereas jmgariepy's suggested ability would require you to remove them both from the same card. I did it this way to allow for odd numbers of thauma counters to still be useful instead of wasted.

The CR rule would add a new special action which does not use the stack and can be taken any time you have priority or are paying a cost. This makes it most similar to a mana ability, without actually being an ability.

I like the thauma counters mechanic in general. I quite liked it first time I read it and realised that the rule was bound to thauma counters. Note that this way there can be sorceries and instants that put thauma counters without needing to grant permanent abilities to their targets.

It seems like the kind of thing development could easily tweak, anyway; perhaps even editing rather than development. More important to playtest it and see whether it turns out too fiddly first.

Oh, one more thing. I like this mechanic. Don't mistake my criticisms for derision; I'm just trying to be helpful.

Though, this does seem like a powerful land. I would argue that you could get away with not adding in the second ability. Just tap to add a counter. I know I'd play it in by Isamaru, Hound of Konda commander deck if that's all it did. I'd understand, however, if you wanted to print a card that pushed the limits of what a land could do, instead of printing a card that was just a variation on Fountain of Cho/Calciform Pools.

Should be uncommon, just because the tracking issues. I had similar problems when I tested my Frozen Delta cycle. It's fun at first, but there comes a point when most players don't want to keep track of this sort of thing. Granted, this isn't as fiddly as the Frozen cycle was... but that card sure taught me a lesson about player patience with abilities that are seemingly marginal.

In fact, I'd say move it to rare. If it's powerful already, then no one would question it being there. That, and it keeps people from feeling they 'have to' play with the card in draft if it comes up. IMO, cards like this should only be played by people who care enough to put them in their decks. Timmies that don't care will be happier to use Plains, even if they are generally weaker.

A separate aside: it seems to me that cards with thauma would be better served if they didn't include reminder text, but instead just included the ability "Remove two counters from ~: Add to your mana pool." Less confusion that way, and less words, too. I mean, unless you have a number of cards that just put thauma counters on random permanents... but a with a quick scan of your set it doesn't look that way.

­Oil Shaman does have a second black mana! That was definitely on purpose. I have actually been poised to move these up to uncommon as soon as I come up with something to replace them; the scaling draw/discard is probably a bit too swingy at common, I agree...I just haven't gotten around to it yet.

Yeah, compared to Pyretic Ritual I thought the tradeoff of losing red might offset the fourth mana, but what with colorless mana mattering in this set, this might need to get pushed to uncommon.