Hanshi Rick Llewelyn performs one of the tougher Shotokan Katas to master, Gojushiho Dai. Similar to it's partner kata, Gojushiho Sho, the "Dai" kata features Keito-Uke ("chicken head wrist block") and ippon nukite (single finger strike) from cat stance.
Core control and pressure down in the stance is critical to performing these techniques well.
For the left leg stability in the cat stance, single leg box squats can be a helpful strength development tool, since the left quad and glute are emphasized in this kata.
Click here for description of each technique, and the Japanese terminology.
And be sure to check out Sensei Ian Abernathy's creative bunkai application ideas: https://www.youtube.com/watch?v=RnOsKGSARdQ