Undertale is an indie role playing game that was created by Toby Fox and released on September 15, 2015 . The game is played on desktop and is sold for $9.99 on the game's website as well as Steam .
Undertale has been ranked #37 on metacritic's Best PC Video Games of all Time with a user score of 7.9 , and has won multiple awards an nominations such as Game of the Year from The Jimquisition and Zero Punctuation, as well as Best PC Game from Destructoid and IGN, among others 
Undertale is a game where you play as a human child that has fallen into the underground – a place where monsters have gone to live after being banished away from the human world. The game tasks you with wandering through the underground, trying to reach King Asgore Dreemurr, the monster that will supposedly send you back home to the human world. Throughout your journey you meet many monsters, and you can choose to either be a True Pacifist and spare them, or fight them and play a Genocide Route.
At first glance, Undertale is simply a game that where players wander around the underground and kill monsters in order to continue on their journey. However, a player can choose to be a pacifist and “spare” the monsters they encounter by solving puzzles  . During these battles the player must determine how to speak to the monster they are “battling” by reading the monsters’ reactions to each option, and essentially talking them into letting them go.
Toby Fox, the creator of the game, seems to steer players into the pacifist direction by giving monsters humorous and lovable personalities that make the player not want to kill them . There is a particular character, Toriel, who players meet early on in the game. Toriel takes the player in and acts as a motherly figure. Eventually the character must leave Toriel’s house, but Toriel doesn’t want to allow it. She becomes the first boss battle of the game, and players must choose to fight or spare her. Sparing is a much harder action to complete, but players often feel a sense of dedication to Toriel and have to make a hard decision between what is easy, and what is framed as the moral option.
Fighting monsters does have a few benefits. Fights are often won sooner, as monsters can only lose HP, and because of this players often don’t have to complete as many stages of the battle as they do when they spare the monsters. Also, when players kill monsters, they gain a higher level of HP.
One of the defining features of Undertale is how “smart” it is. The game remembers every decision the player makes. If a player kills a single monster in any play through of the game, they will never again be able to earn a “True Pacifist” ending . In fact, in subsequent play throughs many characters will mention things about how they remember the player, and perhaps have some preconceived feelings  In this sense, the game acts as a commentary on how once you kill, or even bully, you can never take back your action and in turn you have to deal with the consequences.
The game also acts as a commentary on video game mechanics, as players don’t complete levels in the same way that they would in a typical game. Players do progress through different stages of the game, such as Toriel's Home, Snowdin, and Hotland just to name a few, but they are shown to be on level one until they kill a monster. This makes a statement about how in many video games players must engage in violence. Undertale offers an alternative to this typical aspect, but it still does grant the player a choice in whether or not to engage in violence. The fact that pacifist players don’t gain levels throughout the game (along with not gaining extra strength through HP) can confuse new players and make them feel as though they aren’t progressing in the correct way, but when players do learn what the level number means, it is often too late, and they have solidified their fate and will never be able to be a “True Pacifist”.
Near the end of the game, players enter King Asgore’s castle, and they are met by Sans. Sans takes a look back on how the player has played the game, and becomes a boss battle accordingly. In the Pacifist Route, Sans congratulates the player on their choices and sends them on their way. In the neutral route, he is sad and gives the player a moment to reflect on their actions, but he again lets them pass. In the Genocide Route however, Sans becomes the final boss battle, and is regarded by many as the most difficult boss within the game. In the Pacifist Route, Sans is a very friendly character that always seems to have the player’s best interest at heart, and he has many close relationships to monsters throughout the game, particularly his brother Papyrus. The ways that players interact with Papyrus has a large impact on the way that Sans views and interacts with the player. Killing Papyrus will immediately put the player on Sans’ bad side, but he will not automatically battle them unless they have also killed the other bosses. His good nature is humorous, but his part as the final boss in the Genocide Route also acts as a commentary on how the nicest characters are not always weak. Sans is often underestimated, but is actually very powerful.