Ruins
This is the first character you meet in the Underground, disguised as a talking flower.
Who is Flowey?
This skeleton brother greets you first in the Snowdin forest and is known for his signature catchphrase, "get dunked on!"
Who is Sans?
This royal scientist first appears in Hotland and helps you through her lab with her technological expertise.
What is Alphys?
This main requirement must be met throughout the entire game; the protagonist cannot gain any EXP or increase this stat.
What is LOVE (Level Of Violence) or EXP (Execution Points)?
The player must reach this specific number in each area before confronting the boss to trigger the unique dialogue and encounters of the Genocide Route.
What is the kill counter (or enemy limit)?
This ghostly monster first blocks a path and can be spared by using the "Cheer" action.
Who is Nabstablook?
In the town of Snowdin, this establishment is a popular bar and diner owned by a quiet, flame-headed monster.
What is Grillby's?
When you enter his quiz show, Mettaton asks what robots are made of; the correct answer is this combination of things.
What is metal and magic?
In the post-Neutral run events, Undyne asks the protagonist to deliver a letter to this character, which leads to a date in the Garbage Dump.
Who is Alphys?
Instead of fighting, this first main boss character immediately runs away when the protagonist initiates a battle during the Genocide Route.
Who is Toriel?
The player finds a pile of these sugary items on a pedestal but can only take a few before the pile falls over.
What is Monster Candy?
The innkeeper in Snowdin, a purple rabbit monster, will refund your 80G after your stay for this reason.
What is because you only stayed for "two minutes"?
In the CORE, this monster serves as the gatekeeper to the king, giving the protagonist one last chance to turn back.
Who is Mettaton?
This secret area, located behind a fake bathroom door in Alphys's Lab, is where the protagonist learns about the origins of the Amalgamates and the first human's plan.
What is the True Lab?
This character, usually a major fight in the Neutral and Pacifist routes, is found already dusted by Undyne the Undying during the Snowdin encounter.
Who is Papyrus?
In the first spike puzzle, a sign advises that "Both walk not the middle road," telling the player to step on these buttons instead.
What are the side buttons?
The Lesser Dog encounter becomes famously ridiculous and can be spared by using this repeatedly, which causes its neck to extend to absurd lengths.
What is petting?
This character is fought on the Hotland bridge during the Neutral and Pacifist routes, after blocking your path and attempting to cook you.
Who is Muffet?
This character absorbs all the human and monster SOULs to become the "Absolute GOD of Hyperdeath" and serves as the route's final boss.
Who is Asriel Dreemurr?
The boss fight with this character, a Royal Guardsman who trains in a lab, is widely considered the most difficult battle in the entire game.
Who is Sans?
In the Ruins, if the protagonist decides to call Toriel's name multiple times, this is what she will say.
What is, "My child, please do not do that"?
On a True Pacifist Route, the three white monsters snoring in the Snowed Inn create a song with a melody that is the same as this key track from the game's soundtrack.
What is "Determination"?
As you make your way through the CORE, you pass through a geothermal power plant that provides this to the entire Underground.
What is magical electricity?
During the final battle, the player must use this specific "Act" command repeatedly to remind their friends of their relationships and ultimately save Asriel.
What is SAVE?
At the end of the route, after defeating the final boss, the protagonist makes a "choice" to do this, leading to the destruction of the world and a permanent file modification.
What is erasing the world/universe?