While historically, the gallows associate themselves with prisons. In this case, the Gallows is what allows you to sacrifice another persona to strengthen another. In doing so, it allows a particular persona to move up a level. This is particularly useful especially when you’re trying to gain a certain skill. However, doing so will need you to sacrifice a persona. On a personal note, sacrifice a low level persona in order to not spend too much yen.
Before you use a persona at the gallows, make sure you registered all your persona. Sometimes, you may end up sacrificing a persona that already learned a technique. But because you didn’t register it, you’re going to have to train that particular one again. As is, it will be hard if the persona is very low leveled in comparison to that in Mementos.
However, this feature has certain limitations. One particular limitation is the number of persona you can sacrifice to it. Since the persona can only take so much, a persona can only take one persona sacrifice a day. If you sacrifice any more than that, it will explode due to its inability to accept the influx of power. Also, if you sacrifice a Treasure Persona, you will gain more exp. And if the arcana match, the boost from the persona receives will be a lot more than usual.
The Gallows ability will open at 6/21.