Undertale

Undertale is an independent role-playing game developed by Toby Fox.

Once upon a time, there were two races on Earth: monsters and humans, but a war broke out between them and the latter won. Seven greatest mages sealed the monsters underground and left one entrance through a hole in the Ebott mountain. A lot of time passed since the war, but a human child accidentally falls down the mountain. Its goal is to get back out.

Undertale uses pixelated graphics and traditional mechanics of RPGs such as earning experience points, having an open world, and so on. As the game goes on, the player has to solve several puzzles and interact with NPCs. The battles in the game are represented using the bullet hell mini-games with the player having an option to choose where they want to spare their opponent or hit the enemy back. Monsters behavior depends on the player's actions: if one decides to use a peaceful approach it will be easier to dodge the enemies attacks and vice versa. 

The game features a branching story and several endings. The ending the player gets depends on whether they spared or killed the monsters they encountered throughout the game.