Each Speed Duel GX: Duelists of Shadows Box contains 228 total cards, all usable in Speed Duel:

200 Commons
20 Skill Cards
8 (of 24) Secret Rare Cards
3 of the 8 Secret Rares in every box will be the 3 Sacred Beasts: Uria, Lord of Searing Flames, Hamon, Lord of Striking Thunder, and Raviel, Lord of Phantasms