The two masks hidden in the hub require you to have Rioichi, so you need to rescue him before trying to get them.
#1) Head to the northernmost point on the map. You should find a shuriken sticking out of the ground. Land on it, then use Rioichi's Leaping Dragon technique to jump across to a platform with the mask.
#2) For this one, head to the westernmost point on your map. As with the last one, you'll find a shuriken sticking out of the ground. Use the Leaping Dragon technique to get to the platform with the gold statue, where you'll find the mask.
#3) You need to be on the Breakout! mission. When you have your encounter with Rioichi while he's in the cage, you'll have to crawl through a hole. Before you do that, turn left after passing the two flashlight guards and you'll see a different hole to crawl through, which leads to one of the cells with the mask.
#4) You need to be on the Breakout! mission. After you make it past the gauntlet of swinging blades and fire-breathing dragon statues, you'll slide down a rope using your cane. Climb up to the next area, and you should see a platform you can jump to off to the right of the guard just ahead. Crawl through the hole to find the mask.
#5) You need to be on the Sushi House Startup mission. When you are controlling Rioichi at the beginning and he teaches you how to use the Leaping Dragon technique, use it to get to a railing near the entrance. The mask is over here.
#6) You need to be on the Sushi House Startup mission. This mask is located at the end of the mission. Once you open the third door with the cleaver, don't pull the switch ahead, as this will end the mission. Instead, there's a pipe on your left that you can climb and then jump off of to reach the mask in the air.
#7) You can get this mask during either Something's Fishy or Spiked Sushi. As soon as you enter the caverns, turn around and you'll find the mask by the door.
#8) This mask is found during Pretty in Pinker. When you reach the first area where you must past some water with the Leaping Dragon technique, on the other side, climb the plant to get to the upper area. Use the fans to get across, but before you jump off the last fan, use it to get to the platform in the corner. The mask is in the breakable object in the corner on this platform.
#9) This mask is found during Altitude Sickness. As soon as you pass through the Dragon Gate, a cutscene will occur. As soon as it's over, head back towards the gate and look to your left to find the mask on the ledge. If your back is to the gate, then it'll be on your right.
#10) This mask is found during Altitude Sickness. After Rioichi's cane is stolen, you have to cross a bridge that was destroyed. On the other side are some stairs, and the mask is hidden in the corner to the left as soon as you get to the stairs.
#11) For this mask, you will need to collect all 12 Treasures in the episode to unlock the arcade game in the hideout. Once you do, go to it to play Alter Ego, a twin-stick side-scrolling shooter similar to the hacking mini-games you have played. In the first area, you should see a green portal in a dead end. Go into this portal to be transported to an area with a lot of purple bubbles. The mask will be in the middle of a lot of them.
