So apparently, Famitsu got a short article about Persona Q : Shadow of the Labyrinth. Here's the info (translation found on Dime a Dozen) :
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Its true, the other Persona 3 and 4 party members can now use alternate Personas. Theyre referred to in the magazine as Sub-Personas; whether thats just a means of differentiating the other Personas from their main ones or theres something more to it isnt stated. Apparently in the story they gain this power somehow by way of the two protagonists meeting each other. Details are scarce beyond it having something to do with their Wild Card power allowing it to happen.
Boost meter is built up by exploiting enemy weaknesses. Characters who manage to enter a Boosted state can on their next turn use their skills for free and, if Im reading it right, jump ahead in line in terms of attack priority. The terminology is a bit vague.
Follow-up attacks that are performed when another character has taken their turn and All-Out Attacks have a higher chance of triggering as more and more characters enter a Boosted state.
Party chatter between members can change depending on whos fighting with you. Its not clear if this is just for battles or if it can include conversations outside of fights, too.
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