Go West Young Raccoon
SLY MASK #1
Follow the train tracks south. The first mask is in the area behind the saloon.
SLY MASK #2
Hop aboard the train and ride it to the northern part of the route. There's a high ledge up here accessible only by jumping from the train. Once you've reached it, use the Jailbird costume's ball and chain to knock the crate back. Then scale it to find a Sly mask on a nearby ledge.
SLY MASK #3
Play the mission "Jailhouse Blues" until the point where Tennessee carries the TNT. In the same area, you'll see an outhouse. Bust open the crate inside to reveal a mask.
SLY MASK #4
In the same mission, proceed until you pass the first laser floor. You'll arrive at a large area with a block-pushing puzzle. Upon entering, head immediately left to spot a mask behind some breakable barrels.
SLY MASK #5
During the mission "Cooper for Hire," you'll eventually take control of Tennessee. Play until you pass the first rail sliding section. Just after the rails, you can see a mask on an upper ledge. Clear the enemies from the room, and climb up the boxes to reach the mask.
SLY MASK #6
Near the end of the same mission, you'll spot a multi-targeted crate just before the final rail. Use Tennessee's Crackshot ability to shoot every target at once, destroying the crate and revealing another mask.
SLY MASK #7
This one is found during "Saloon Bug." Proceed until you reach the casino area as Sly. The mask is atop the rotating wagon in the middle of the room. Use the cane launch move to scale it.
SLY MASK #8
Play the mission "Jail Break" and proceed until the second gate Tennessee must lower. Just before taking the zip line back to the boat, climb down the nearby rope to find a mask below.
SLY MASK #9
This mask is found during "Operation: Gold Digger." Once in control of Tennessee, you'll enter a laser-filled train car. As you proceed, you'll reveal a mask behind a destructible crate. After deactivating the lasers, backtrack a few steps to grab it.
SLY MASK #10
In the very next train car is another mask. Once again, deactivate the lasers and backtrack a bit to grab it.
SLY MASK #11
Once you've recovered every treasure in the level, the arcade machine in the hideout will be repaired. Boot it up to play System Cracker. In the second arena, grab the purple panzer power-up and head to the right. Use the cannon to blow the wall away, revealing a hidden area containing a mask.
Note: For more detail on collecting the treasures required of this mask, see our Sly Cooper: Thieves in Time treasure locations guide.