Shifting stones are fulcrums of natural power that tap into the pervading essences of Orboros to alter the flow of battle radically. Their mysterious power allows them to bathe nearby allies in raw life essence, sink quickly into the earth and rise again wherever they are needed, or send another creature to a completely different area of the battlefield.
Stone keepers are unwavering devotees of the earth-shaping path of druidic magic. These stoic blackclads share a deep connection with the magic-infused stones of the Circle. Calling upon the earth itself to do their bidding, stone keepers enshroud their rocky charges in mystical fog, shower their foes with a hail of rock, or warp their own flesh to stone-like rigidity.
The Shifting Stones are fury management, heal your models, let your models teleport, and generally provide a lot of flexibility. You can even take them in every theme, so you should always have at least 1 unit.
Thoughts on adding the CA
The Stone Keeper is odd. But he is very cheap to include in an army. The positives for taking him are...
He increases the units CMD tremendously, allowing them to spread out their healing ability and more easily get a model into the teleportation triangle.
He can also trigger the healing due to the wording
He grants the unit Prowl and is the only model in the unit with attacks.
The Negatives are...
The stones don't especially care about prowl, since they are hard to shoot off the table already, though it does make it harder for opponents to pick off a lone stone.
his spells aren't very useful, either they prevent him from getting picked off, or they provide a not particularly accirate short range AOE with a crit knockdown. If the unit is close enough to use that, something has probably gone wrong.
He increases the units cost by 33% without really improving the bits that make the shifting stones good.
Combos & Synergies
Any beatstick likes to be teleported straight into the enemy's face. Charging is better if you can since most opponents won't leave a better opening for you to teleport into though. Wold Guardians are the only beasts that gain any additional distance over charging from being teleporte
Construct warbeasts. Healing them is especially useful, and they can struggle to remove fury since they can't frenzy.
Morvahana2 & Baldur2 - both are very likely to hurt themselves and enjoy consistent healing.
Stone Keeper Synergies
Although he isn't game breaking the Stone Keeper does have in faction Synergies and opens up a few more combos for the unit.
Kaya3 & Morvahana2 both have fog of war, reliably granting concealment to trigger prowl.
They're useful to block charge lanes and contest zones, due to their high ARM, boxes, and inability to be moved by anything. Many a game was saved by a stone contesting a zone.
If one stone dies, they can't teleport other models. But they still can move themselves, so jam them into the enemy.
Remember you can teleport a model that has already moved. This is especially useful for your warlock since you can play a bit farther forward to cast spells and catch more stuff in a feat but still move them to safety afterwards.
Keeping them with a beast that is playing forward can be useful, if your opponent can't finish the beast off the stones will be able to fix any damaged aspects, and the beast will be able to use more fury with the stones around. An unsure opponent may commit attacks to the stones potentially saving your beast and giving you more attacks.