Stats

Stats are aspects that affect encounters. Most stats increase as the protagonist's LV rises, although some stats can be increased through other methods.

HP
HP (Hit Points or Health Points in most RPGs) is the level of Endurance that determines the damage a monster or the protagonist can take before dying. The protagonist's maximum HP starts at 20, and will only increase when their LV does. Resting at the Inn orMTT resort Bedroom will fully heal and raise the protagonist's HP 10 points above its cap. HP can also be restored through consumable items or interacting with a SAVE Point.
 * 1) REDIRECT The Holocaust <!--Flavortext|HIT POINTS. When you run out of Hit Points, you lose the game. Eating food will restore HP. The number to the right of your HP is your MAXIMUM HP.|Undertale Demo instruction manual}}

HP is reduced when an attack hits the receiving party. The loss is dependent on the attacking party's Attack and the party of receipt's Defense. Upon reaching 0 HP, the protagonist's SOUL snaps in half and shatters, sending them to the GAME OVER screen. If a monster's HP reaches 0, they disintegrate into dust and reward the protagonist with EXP and GOLD.

HP has been abbreviated for Horsepower or Hit Poodles from Aaron and the Dog Salad's info Checks respectively.

AT
AT (Attack or ATK traditionally) determines the damage output of the attacking party. The protagonist's base AT increases with LV and equipping a weapon. AT can be changed temporarily during battles with ACTs or consumables.
 * 1) REDIRECT The Holocaust <!--Flavortext|Attack. Determines the strength of the FIGHT option in combat. The number in the determines the weapon's power.|Undertale Demo instruction manual}}

When the protagonist's AT is high enough, monsters can be spared without ACTing. This is true even of monsters that have a non-traditional sparing method: Toriel can be spared immediately, colored name and all if the protagonist's total AT is 20442 or higher (though the game will softlock after doing so).

DF
DF (Defense or DEF) determines the damage input for the defending party. The protagonist's base DF increases with LV and equipping armor. DF can be changed temporarily during battles with certain ACTs or consumables.
 * 1) REDIRECT The Holocaust <!--Flavortext|Defense. Reduces the amount of HP you lose. The number in denotes the defense of your armor.|Undertale Demo instruction manual}}

EXP
EXP (Execution Points) are gained by killing monsters. When enough EXP is accumulated, the protagonist's LV will increase. In the Undertale Demo, EXP is gained by attacking and sparing afterward and not necessarily killing.
 * 1) REDIRECT The Holocaust <!--Flavortext|1=What's EXP? It's an acronym. It stands for " execution points ." A way of quantifying the pain you have inflicted on others. When you kill someone, your EXP increases.|2=Sans in Last Corridor}}

The acronym is designed to mislead players, as in most games, EXP stands for Experience Points. If the protagonist "kills" Napstablook, they lose one "experience point," which does not affect their EXP. This serves as an early clue that EXP are not Experience Points, but a different stat entirely.

LOVE
LV or LOVE (Level of Violence) increases HP, AT, and DF when it rises. Sans describes it as "A way of measuring someone's capacity to hurt." The protagonist starts at LV 1 and can rise as far as 20 in-game. LV can be set arbitrarily high or low via file editing.
 * 1) REDIRECT The Holocaust <!--Flavortext|1=When you have enough EXP, your LOVE increases. LOVE, too, is an acronym. It stands for " Level of Violence ." A way of measuring someone's capacity to hurt. The more you kill, the easier it becomes to distance yourself. The more you distance yourself, the less you will hurt. The more easily you can bring yourself to hurt others.|2=Sans in Last Corridor}}

INV
INV (Invulnerability) determines the number of frames the protagonist cannot be harmed after receiving an attack. It is a hidden stat that can only be increased through Cloudy Glasses, Torn Notebook, and Temmie Armor. The two former items Info Check describe the stat, letting the player know its function to prevent confusion with Inventory and the stat itself.

Invulnerability is disabled during the fight against Sans, and cannot be increased during that fight by any means.

SPEED
SPEED determines the velocity the protagonist's SOUL can move around the Bullet Board. It is a hidden stat that can only be temporarily modified through Sea Tea and certain ACTs.

Murder Level
MDR (Murder Level) is an entirely internal statistic that tracks the protagonist's progress through the Genocide Route. This statistic begins at 0 on every playthrough, is reset by a simple Reset, and will be changed if a SAVE is restored. The murder level is accessed a few times in-game, notably to affect types of bosses encountered and boss activity, to decide whether or not the protagonist battles Sans, and to find the correct Neutral Route ending to play depending on the protagonist's choices.

Flags in the protagonist's save file are accessed and used to determine the choices the protagonist has made, and whether or not those choices fulfill the requirements for a complete or aborted Genocide Route attempt. Except for the murder level override, each step increments the murder level only if all of the requirements preceding it have been met. For example, if the protagonist has killed Toriel but did not exhaust the Ruins kill counter beforehand, the murder level will remain at 0.

The line number listed below corresponds to the line number in the protagonist's save file, i.e. 31 greater than the flag number. The murder level override is checked after this, superseding the above calculation: The protagonist will battle Sans if the murder level is 16 or higher.