
I think this card is probably most comparable to Strange Solution. Both require one action to use and some form of test. (Strange Solution has the test built into the card itself, while Ancient Stone requires an investigate action (which is not always a test but usually is)). However, Ancient Stone is much more difficult to use because:
- It requires 1 experience to include into the deck, making the whole upgrading process at least 1 scenario longer.
- You actually want the test to be difficult to get more out of the upgraded versions.
However, if you can pull off the early legwork to get this going, a properly-researched Ancient Stone can be upgraded into some really powerful tools. With a lot of secrets on it, Ancient Stone (Heart of the Elders) can deal a lot of testless damage to monsters, which is amazing in this game. Ancient Stone (Minds In Harmony) is also one of the most efficient ways of healing horror in the game, which makes it a great option for Carolyn Fern (particularly if she has Shrewd Analysis).
There's been some discussion around using Double or Nothing to create an absurdly high skill test. While this is fine, Rogue cards and Seeker cards rarely show up together for the same investigator, so that can take some coordination and it might not be worth the extra effort, since the stars really have to align. However, I have found some success in using 2 copies of Drawing Thin to increase the difficulty by 4, which is still a sizeable amount. Drawing Thin is useable by Minh Thi Phan and Rex Murphy - two investigators that can get a lot of use out of the Ancient Stone - so I think there's good combo potential there. That's to say nothing about how Drawing Thin lets you draw cards before a skill test when you activate it, which means it will be useful even after you use it to boost up the Ancient Stone test number.
Overall, while this is a tough card to play and get set up, I think it is probably worth the investment. I think the new Drawing Thin makes it a lot better, particularly if you are also running Higher Education in non-Taboo scenarios.