The Mid-Starboard Hallway introduces a new mechanic that's unique to Shido's Palace: mouse statues. As Futaba explains, various rooms in the hallways have Shido statues that emit fields that turn the Phantom Thieves into mice. This "mousification" will end as soon as the Thieves leave the room, but as mice the Thieves have a fraction of their attack and defense scores and can't use their Personas. As such, players should avoid Shadows in these areas at all costs.