You'll first encounter the statue riddle in Elden Ring: Shadow of the Erdtree while exploring the Shadow Keep. If you find your way down to Shadow Keep, Back Gate site of grace, you'll discover a small room with a headless Marika statue and a riddle: Have mercy. For the spirited-away shamans. This might seem a little confusing at first, but upon closer inspection, you'll realise there's a passage behind the statue.
If you read the notes that kindly players have left nearby, you'll also discover that you need to use a gesture in order to pass through into the secret area beyond. Here, I'll explain where to find the gesture that you require, and how you were even supposed to know where to get it in the first place.
How to solve the 'Have mercy. For the spirited-away shamans' riddle
You can find the gesture that you need in the Bonny Village on the east side of Scadu Altus. You might recognise this location as the village with the hanging pots you can spy from the plateau above. To access it, you need to find the Moorth Ruins and head down into the smaller of the two holes by the church. Traverse the tunnels—watching out for Hornsent enemies—and you'll emerge from the village well.
The gesture in question is called O Mother, and you can find it a little way north of the village alongside the ravine, before the first bridge that leads to the Whipping Hut. You'll spot a headless corpse posed in the gesture, so just run up and grab it. Now, how were you supposed to know to get the gesture here? If you continue onto the Whipping Hut, you'll find a spirit who reveals that it's the destiny of all shamans to go in the pots, and the area beyond the statue will reveal even more about that.
Simply head back, use the O Mother gesture in front of the statue, and shortly after it'll slide open.