A planar-part-based toy assembly set includes planar parts that have different shapes and are made by stamping a planar material board. The planar parts include a body piece and a limb piece. The body piece has a slotted ring for coupling with the limb piece. The slotted ring has a cutting slot, a narrow section and, a wide section. The limb piece has a closed ring, or a slotted ring as stated above. The closed ring of the limb piece can pass through the cutting slot of the slotted ring of the body piece and be mounted around the narrow or wide section of the slotted ring. When the closed ring is around the narrow section, the limb piece can freely swing, and when the closed ring is around the wide section, the limb piece is fixed at a specific angle, which can be later adjusted by the player.