Wonder Boy III: The Dragon’s Trap is a side-scrolling platform game and action role-playing game in which the player controls Wonder Boy as he looks for the Salamander Cross that is hidden by the Vampire Dragon in Monster Land. The player uses the directional pad to move Wonder Boy left or right, crouch down (only possible with Hu-Man or Lizard-Man), or by entering doors by holding up. Players use the buttons on the game’s controller to attack enemies and to jump. Wonder Boy can attack with his main weapon or with a secondary weapon by holding down on the directional pad and by pressing the attack button. Pressing the pause button brings up the Status Screen and pauses the game if Wonder Boy is fighting a dragon.

Wonder Boy has a life meter represented on the top of the gameplay area by a series of hearts. The hearts turn from red to black when Wonder Boy sustains damage from enemy attacks, and he dies when all his hearts turn black. If the player has a life potion (“medicine vial” in Dragon’s Curse) remaining, Wonder Boy will revive with some of the hearts refilled; the number of life potions remaining are displayed on the top of the gameplay area next to the life meter. If the player does not have any life potions left, the game ends, and the player is taken to a “continue screen”; there the player has an opportunity to earn a free life potion if the cursor surrounding the border of the continue screen lands on a red heart (or a red vial in Dragon’s Curse). After that, the player continues the game, starting at the town again. Players can visit the town’s church to receive a password so that they can continue the game at a later time after turning the system off. The password saves the current player’s form, equipment, and amount of gold; but it does not save any secondary weapons or life potions in stock. They can input the password from the game’s title screen. Dragon’s Curse, has a “file cabinet” which allows players to store passwords into the game’s memory; the player may access these stored passwords and continue the game without needing to manually input them.

After completing the first level in the game – which is the same as the final level in Wonder Boy in Monster Land – the player begins from a town in Monster Land as Lizard-Man, and the gameplay becomes nonlinear in the same style as Metroid. From there, the player explores and finds items and clues needed to access different parts of Monster Land. After defeating enemies, they will drop gold or secondary weapons in which the player can collect by touching them. Players can also find gold and items by opening treasure chests. With gold, players can buy additional items in shops or restore their life meter in hospitals. Shops, normally designated as doors with windows on them though some do not, are located in town or in caves and allow players to buy better equipment. Players must have enough gold to buy an item in a shop, and items with question marks displayed mean that they cannot buy the item due to not having enough charm; players can collect Charm Stones to increase charm or equip certain items in order to buy them. The Status Screen shows how much attack and defense power, and charm that the player has in the form of “points”; the higher the points, the more of that attribute the player has. The amount of attack, defense, and charm depends on the player’s form and with what the player is currently equipped; stronger swords increase attack power, stronger shields and armor increase defense power, and collecting charm stones and equipping specific types of armor increase charm.

Throughout the game, players will go through differently-themed levels: underwater, desert, jungle, cave, and sky. At the end of each level is a different dragon. After defeating a dragon, the player character changes form, and his abilities change. The player can assume six different forms throughout the game. Wonder Boy begins the game as Hu-Man, equipped with all eight hearts and the strongest equipment. He turns into Lizard-Man after defeating and being cursed by the Mecha Dragon (Some sources refer to this creature as the “MEKA dragon”.) in the first level. At that point, he loses all equipment and all hearts except one. Lizard-Man attacks enemies by breathing fire at them, and he can duck. Mouse-Man can walk on walls and ceilings designated by checkered “mouse blocks”. Piranha-Man can swim freely underwater and can access underwater places which the other forms cannot. Lion-Man attacks enemies with his sword by swinging from directly above to directly below him. Finally, Hawk-Man can fly freely in the air but sustains damage if he enters water; he can access places in the sky which the other forms cannot.