CTMA Centre is essentially a toy mall. You head inside and it doesn't take much wandering before you spot a toy store, and then another one, and so on and so forth. After a few minutes you will be so overwhelmed with the amount of toy stores, that you won't know where to start. But I suggest two spots in particular, both of which are among my favorites.
The best stores at CTMA are by far Toy Hunters and Superman Toys. Toy Hunters is the main spot for Hot Toys. They sell other brands as well, but there's definitely a focus on high end 1:6 figures. Superman Toys has all sorts of goodies and is one of the more spacious stores in the mall. When entering be sure to catch a glimpse of the massive toy display to the right, or you can just see it here.
Other small shops with typical glass displays housing a menagerie of merchandise are spread throughout, very much like this one here. They tend to carry less high end stuff and in smaller volumes, as the shops are smaller. Blindbox figures and other small toys are typical. Shop around to get the best deal.
CTMA Centre is at the corner of Sai Yeung Choi Street and Dundas Street. The general area or neighborhood where it's located is called Mong Kok. Aslo, VERY IMPORTANT to note that shops open late, so don't venture out too early. Going after 12 PM ensures at least the major one's will be open. That's more help than I had so you should be alright. Good luck!
Be sure to also take a stroll across the street from the CMTA Centre, as there is another excellent shop there, called ANIMATE. It's on the second floor of the building directly across from CTMA. You can't miss it because of the large window display of various character statues.
Not too far away is the world famous UML (Universal Models Ltd.). This place is a Hong Kong toy institution. CTMA Centre is serious business, but this is the place that toy hunters and regular folks alike hit up. It's especially worth it if you enjoy model building. The main store houses Gundam kits and a variety of toys on the second floor, and a small capsule machine area on the first floor. Next door, they have a another store with car, plane, and military model kits. It's hard to find so ask the staff. The official address of the main door is: G/F-2/F, 579 Nathan Road, Mongkok, Kowloon, although it's more like around the corner from Nathan Rd. The main door is actually on Dundas St. (around the corner from the large UML billboard- as seen below).
Toys "R" Us Kowloon