Toriel

Toriel is an important non-player character in Undertale. Like all residents of the Underground, she is a monster: a race of sentient creatures sealed away long ago by a magical barrier crafted by humans. She first appears to save the player from Flowey's vicious attacks and guides them through the subterranean Ruins, the monsters' first "Home" upon their exile to the Underground. Toriel also teaches players how to resolve encounters non-lethally. Although she cares deeply for all humans who fall down into the monster realm, Toriel is reluctant to allow the player to leave the safety of the Ruins and will eventually block their exit with a boss battle.

During the fight, Toriel will deliberately avoid killing players with her magical attacks while also attempting to persuade them to turn back. Killing Toriel causes her to remark on the player's strength and warn them of Asgore Dreemurr's plan to take their soul in order to shatter the magical barrier sealing the Underground. If the player spares Toriel, she stands aside and allows them to leave the Ruins peacefully, but also asks players not to return. Additional dialogue acknowledging Toriel's demise occurs if the player kills her, reloads from a prior save point and then begins the fight once again; however, Toriel herself seems unaware of the player's ability to "SAVE". The player can also perform an instant kill against Toriel by repeatedly "Spare"-ing her during the battle until she ceases attacking, and then selecting the "Fight" command after her guard is lowered.