Stats are aspects that affect encounters. Most stats increase as the protagonist's LV rises, although other methods can increase the stats.
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 only increases when their LV does. Resting at the Inn or MTT resort Bedroom fully heals 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.
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
An attack hitting the receiving party lowers their HP. 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.
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.
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, the protagonist can spare monsters without ACTing. This rule is true even of monsters that have a non-traditional sparing method: Toriel can be spared immediately, and the colored name and everything else shows if the total AT is 20442 or higher (though the game softlocks after doing so).
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.
Defense. Reduces the amount of HP you lose. The number in () denotes the defense of your armor.Undertale Demo instruction manual
DF is subtracted from the damage output of the attacking party. However, it cannot lower the taken damage to a value less than 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.Sans in Last Corridor
EXP (Execution Points) are gained by killing monsters. When the protagonist accumulates enough EXP, their LV increases. In the Undertale Demo, EXP is gained by attacking and sparing afterward and not necessarily killing.
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 and serves as an early clue that EXP are not Experience Points, but a different stat entirely.
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.Sans in Last Corridor
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.
INV (Invulnerability) determines the number of frames an attack cannot hurt the protagonist after they receive one. It is a hidden stat that the protagonist can only increase through the Cloudy Glasses, Torn Notebook, and Temmie Armor. The former two items explain INV in their Info check.
SPEED determines the velocity the protagonist's SOUL can move around the Bullet Board. It is a hidden stat that the protagonist can modify temporarily only through Sea Tea, certain ACTs and in a fight with Vulkin using the Thunder attack.
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 and is reset by a simple Reset. 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 fulfilled. For example, if the protagonist has killed Toriel but did not exhaust the Ruins kill counter beforehand, the murder level remains 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.
|Flag||Line||Setting||Action to set flag||Murder level set to...|
|202||233||20 or greater||Killed 20 or more Ruins encounters||1|
|53||84||1||Killed Dogamy and Dogaressa||4|
|54||85||1||Killed the Greater Dog||5|
|203||234||16 or greater||Killed 16 or more Snowdin encounters||7|
|252||283||1||Killed the Glad Dummy||10|
|204||235||18 or greater||Killed 18 or more Waterfall encounters||11|
|251||282||1||Killed Undyne the Undying||11, evaluate below|
|350||381||1||Killed Undyne, in any form||12, if above is true|
|402||433||1||Killed the Royal Guards||13|
|205||236||40 or greater||Killed 40 or more Hotland encounters||15|
|425||456||1||Killed Mettaton (NEO)||15, evaluate below|
|27||58||Must remain 0||Have not spared any mini-bosses, such as Lesser Dog||16, if above is true|
The murder level override is checked after this, ignoring the above calculation:
|Flag||Line||Setting||Action to set flag||Murder level set to...|
|26||57||1 or greater||Must be set manually, by editing the flag or pressing M in debug mode||Setting|
The protagonist battles Sans if the murder level is 16 or higher.
|LV||HP||AT||DF||EXP to next LV||Total EXP to LV|
- When the protagonist enters a battle with an LV of 20, their AT and DF automatically sets to 30 and their maximum HP to 99. This change is never seen in-game because the only instance of the protagonist's LV getting to 20 is after their battle with Sans, who is the final opponent the protagonist can practically fight.
- ↑ When Sans is met in the hallway, murder level is calculated. If it is greater than 16, the fight occurs. – Reddit
- ↑ Decompiled Undertale code