While some RPGs present nonviolence as a series of choices in a text tree which might let you sidestep combat, Undertale integrates them into its turn-based battles. You can attack, but for each monster you can instead perform various actions, like “Compliment” and "Threat", which might help pacify them.

During the enemy's turns you control your Soul, a tiny red heart, and must dodge monster attacks in a brief bullet-hell sequence. Boss battles often change the mechanics of dodging by painting your Soul a different colour – when it's blue, for example, your Soul is subject to gravity and can jump. It's a simple enough system, but manages to stay fresh for the whole game.

The morality of Undertale leaves no room for ambiguity or nuance, but the game's dedication to it is what stands out. Forming deeper friendships with the strange and entertaining monsters of the underground is interesting and rewarding; killing them feels terrible, and the rest of the cast won't let you forget.

The game even reserves a special kind of hell for any player who would go out of their way to kill everyone “just to see all of the game's content...”

While the game's art is rather simple, the music is outstanding. It's a memorable and catchy mix of chiptunes and piano, weaving various themes throughout its tracks in many different styles. Having made the game all by himself, Toby Fox manages to fully utilise every visual, audio and technical aspect available to convey the desired narrative and tone.

Knowing more beforehand would spoil the fun. Undertale is not a long game – you'll beat it in about five hours – but it's an immensely clever game, full of surprises and worth replaying. It's a worthy successor to its clear influence, the Mother/Earthbound series, and I can't wait to see what kind of games will inherit Undertale's influence after its stunning success.