Rex, known as Ryuzaki (エスパーろば Ryūzaki) in Japan, is a character in Yu-Gi-Oh! Duel Monsters 4: Battle of Great Duelist. This is a video game depiction of Dinosaur Ryuzaki from the manga.
Rex is a Stage 1 opponent available from the start. By defeating Rex and the other Stage 1 opponents five times each, the player can unlock Stage 2.
Rex's Deck contains a number of Earth monsters. It includes "Sword Arm of Drago", "Megazowler" and "Red-eyes B. Dragon", all of which were used by his manga counterpart.
The following cards can be won, by defeating Rex. The chance of winning a card is indicated by the "%" (chance out of 100) and "2048th" (chance out of 2048) columns.