Can someone please explain to me in laymans terms, how does the Army Across Time spell combo with the Coven Hex?
The idea is that you cast the spell, create as many copies as possible, and each one uses it's action to increase your caster level by one. This boosts your caster level and you use the additional caster levels to summon more copies.
This requires some weird rules interpretations.
1. That your copies get your hexes.
2. That when your caster level increases, the spell level of on going spells increase with it.
3. That your DM in no way limits how many free actions you can take in a turn.
For the most part they don’t interact because the spell is not on the list of any caster capable of casting the spell. The only way I know this could work is if you are playing a Samsaran alternative racial trait Mystic Past Life. There may be another way, but I am not aware of it.
The spell states that the duplicate has your statistics so it should have your hexes. Coven hex allows someone with the hex to use the aid another action to grant a +1 bonus to the other witch's caster level. The spell allows your duplicates to use the aid another action once. The spell also limits you to having one duplicate per 3 caster levels you have.
So, if you do manage to get both the spell and the hex on the same character you can do the following. Cast Army Across time after this you can use as many free actions as your GM permits to summon duplicates, up to 1 per 3 caster levels. When you cast another spell, each duplicate can use an aid action to boost your caster level for that any spells cast in that round at which point those duplicates disappear. This boost does not apply to any existing spells including Army Across Time. Each round after that you can use another free action to summon up as many duplicates as your GM allows free actions. You can still only have a maximum of 1 duplicate per 3 caster levels at any one time. As long as the spell has not expired, and you still have duplicates left they can use an aid another action to boost your caster level.
If you were a literal/actual Hag, and casted Army Across Time... poof, COVEN... a Coven requires 3 Hags and Aid Another. I'd allow it, but if it was a single Hag tapping into power she should be otherwise unable or somehow banned from using, there will be consequences. Most abilities allowing you to count as a Hag say there has to be an actual Hag, so this only works with real Hags that are weak or otherwise exciled...
For the most part they don’t interact because the spell is not on the list of any caster capable of casting the spell. The only way I know this could work is if you are playing a Samsaran alternative racial trait Mystic Past Life. There may be another way, but I am not aware of it.
Shadow Patron grants Shadow Conjuration of which Army Across Time is a valid option
It doesn't look like you need to be in a coven for it to work. The ability to join a coven is separate from the ability to aid another for a caster level bump. Or I'm missing something, which is entirely possible.
There's quite a few ways to get the ability to aid another for a caster level bump, but the vagueness of "statistics" in the army across time spell means we don't know for sure what exactly the caster's duplicates can bring to the table.
The coven caster feat is unlikely since the spell specifically calls out teamwork feats, which coven caster is not.
The coven hex seems possible.
The accursed blood line's arcana seems possible.
The Hag-Called psychic discipline seems possible
The coven hex version gets more attention due to some people interpreting the scar hex as functioning with the aid another action granted by the hex. That would lead to other weirdness though, so I doubt it's an intended interaction(Scar+nails or scar+cook-people).
^I think Iron Collar of the Unbound Coven will sufficiently approximate this to work. The item doesn't technically have the Evil description, but it sounds pretty evil.
Coven (Ex): The witch counts as a hag for the purpose of joining a hag's coven. The coven must contain at least one hag. In addition, whenever the witch with this hex is within 30 feet of another witch with this hex, she can use the aid another action to grant a +1 bonus to the other witch's caster level for 1 round. This bonus applies to the witch's spells and all of her hexes.
The In Addition specifies that the ability to use aid another action does not require you to actually be part of a coven. This is why the leadership feat is one of if not the best feat a witch can take. Who cares about the cohort what matters is you have a bunch of other witches boosting your caster level.