1 Go to the painting room
The painting room can be found in the eastern side of the Mansion (1F). The entrance to it is in the corridor that has the knob-less door.
2 Turn the 2nd switch on
Go to the yellow painting near the door that says 'a picture of a valiant wearing a bracelet'. Click on the switch and the painting will turn orange.
3 Turn the next switch on
Go around the corner until you find another yellow painting that says 'a picture of a saint wearing a crown'. Click on the switch and the picture will turn green.
4 Turn the 3rd switch on
Go to the end of the corridor until you find a red painting that says 'A picture of a sage wearing a necklace'. Click on the switch and the picture will turn purple.
5 Hit the final switch
Go to the main painting at the end of the corridor and press the switch.
6 Grab the death mask
The painting will move up and you will be able to walk through the wall to get the death mask found on the floor. See how to get all death masks.
7 Beware of the right order
If you don't press the switches in the proper order, the crows will attack you. Make sure to maintain the right order.