Kaeru no Tame ni Kane wa Naru, also known as "For the Frog the Bell Tolls" is an action-RPG developed by Nintendo and released for the Game Boy in 1992. This obscure Japan-only action RPG was the basis for several key gameplay elements in Link's Awakening. The player takes on the roll of Prince of Sabure who, along with his childhood rival, Prince Richard, embark on their quest to rescue the Princess of Mille-Feuille, whose kingdom has been invaded by the Croakian army led by King Delarin. The game received an English fan translation in 2011.
Gameplay is a mix between an action-RPG and platformer. The player initiates combat by walking into enemies in the world, where a fighting animation plays out and the two characters fight automatically until there is a winner. The winner is dependent on who has the most defense and offensive abilities, each character will do an amount of damage (taking away heart pieces) per turn and in the case of standard enemies, there is no interaction beyond combat initiation. The player can increase their skills by picking up objects that increase health, speed and strength and by purchasing items such as better shields. As there is no skill in combat itself, the strategy involves choosing which enemies to fight and which ones to avoid. If the player has too few heartpieces, they will have to fight weaker enemies in the hope of obtaining hearts, drink wine that can be purchased from the town, or go back to the town and visit a doctor. If the player dies, they are sent back to the doctor in the nearest town.
The other part of the game is platforming in the game's dungeons, which is where the unique feature of the game comes into play. During the course of the game, the Prince is transformed into a frog. A frog can jump higher, instantly defeat small enemies by eating them (receiving a health bonus) and swim in water. Frogs cannot do any damage to larger enemies and will thus lose in a fight to them. The player can only turn into a frog by entering water and can transfer back to a human by eating Joy Fruit. The player also receives the ability to transform into a snake, who can get into small nooks that the frog and human cannot gain access to, however their jumping is extremely low. Unlike the frog, the player can transform into the snake at any time by eating a snake egg. Like the frog, the player can transform back into a human by eating Joy Fruit. Several areas in the game require the player to use all 3 forms in conjunction to solve a particular puzzle.