Warpstone Flux Rating: ⭐️⭐️⭐️ 3/5 stars. Situational and average rules.
The Anathema Psykana Army List is very limited to say the least. There are only a few units - we will review these distinctly - which does not give a lot of flexibility. As they are also Talons of the Emperor, they can be allied to a main Custodes force, which is reasonable, or any other Loyalist force.
The Silent Sisterhood can also be the primary detachment. In which case the army gets one bonus reaction point so long as you have someone with the Investigatus Militant trait (which is essentially either Jenetia Krole, or a Knight-Centura -- undoubtedly a player will have one of these in a primary force!).
As for the main perk, their Divisio Tactica is Anathema. This means that they are immune to psychic damage and warp damage. They cannot be targeted by friend or foe for blessings or curses. All damage from things like psychic powers and perils of the warp is simply ignored. End of. Further, if someone tries to wound them with a psychic weapon or immaterium weapon, then they only do so on a 5+.
Overall, this is - as you would expect - an anti-psyker, anti-daemon, and anti-sorcerer army. They could do well against certain builds (notably daemons, Thousand Sons, certain Word Bearers, and others). But against more regular armies like traitor Death Guard who might shun psykers, their only boon is realistically the additional reaction point. Hence I would give them a much higher star rating against certain armies, and a much lower one most of the time. Which is why I've given 3/5 stars overall as a bit of a compromise position.


