Undertale is Toby Fox's 2015 role playing game about a child who falls into the Underground and has to find a way out. Its hook is that every encounter can be ended without killing: you dodge patterned attacks inside a small box, then use ACT and MERCY instead of FIGHT. A single run takes roughly six to seven hours, and the game quietly records what you chose to do along the way.
Combat in Undertale rewards knowledge over reflexes. Understanding how each mechanic works (and how they interact) is what turns a struggling player into a dominant one. New here? Start with our beginner's guide for the basics.
Core Combat Mechanics
1. Bullet dodging in the SOUL box
On an enemy turn your SOUL becomes a small red heart inside a rectangular box and you dodge projectile patterns with the arrow keys. You start on 20 HP, so two or three clean hits from a mid game attack is fatal.
Why it matters: This is the foundation of all combat. Everything else builds on this.
2. FIGHT, ACT, ITEM and MERCY
FIGHT uses a timed bar where stopping the cursor dead centre deals maximum damage. ACT holds enemy specific options like Check, Flirt or Compliment, and using the right ones turns the enemy's name yellow in the MERCY menu so it can be spared.
Why it matters: The most underrated mechanic. Players who master this early have a massive advantage.
3. LOVE, EXP and LV
EXP stands for Execution Points and LV stands for LOVE, and both rise only when you kill. Staying at LV1 keeps you on 20 HP for the entire game, while LV20 puts you on 99 HP, so it is a difficulty setting as much as a moral one.
Why it matters: Unlocks a new layer of gameplay depth once understood.
4. Coloured SOUL modes
Several bosses recolour your SOUL and change the rules entirely. Blue drops you to the bottom of the box so you jump, green pins you in place behind a directional shield, yellow lets you shoot back, and purple traps you on horizontal lines.
Why it matters: The tactical edge that separates average players from advanced ones.
5. Route tracking across a whole run
The game counts kills, spares, deaths and dialogue choices, and it holds those counts across saves. Which of the three main endings you reach depends on what those counters say when you get to the end.
Why it matters: The endgame optimization mechanic. Small improvements here compound into massive gains.
How These Mechanics Combine
Understanding how mechanics interact is where real optimization happens:
Bullet dodging in the SOUL box + FIGHT, ACT, ITEM and MERCY
On an enemy turn your SOUL becomes a small red heart inside a rectangular box and you dodge projectile patterns with the arrow keys. When combined with FIGHT, ACT, ITEM and MERCY, fight uses a timed bar where stopping the cursor dead centre deals maximum damage. This combination is the core of every effective build.
LOVE, EXP and LV + Coloured SOUL modes
EXP stands for Execution Points and LV stands for LOVE, and both rise only when you kill. Paired with Coloured SOUL modes, several bosses recolour your soul and change the rules entirely. This is why the tier list favors builds that leverage both.
Route tracking across a whole run as a Multiplier
The game counts kills, spares, deaths and dialogue choices, and it holds those counts across saves. Which of the three main endings you reach depends on what those counters say when you get to the end. This system amplifies everything else. The better your Route tracking across a whole run optimization, the more your other mechanics pay off.
Combat by Build
Each build approaches combat differently:
Neutral Route (A-Tier)
Combat approach: Balanced combat style. Key equipment: Stick Primary mechanic: Bullet dodging in the SOUL box
Neutral Route offers a solid combat experience. Full setup in our builds guide.
True Pacifist Route (A-Tier)
Combat approach: Balanced combat style. Key equipment: Toy Knife Primary mechanic: FIGHT, ACT, ITEM and MERCY
True Pacifist Route offers a solid combat experience. Full setup in our builds guide.
Genocide Route (A-Tier)
Combat approach: Balanced combat style. Key equipment: Worn Dagger Primary mechanic: LOVE, EXP and LV
Genocide Route offers a solid combat experience. Full setup in our builds guide.
Hard Mode (A-Tier)
Combat approach: Balanced combat style. Key equipment: Burnt Pan Primary mechanic: Coloured SOUL modes
Hard Mode offers a solid combat experience. Full setup in our builds guide.
No Hit Challenge Run (A-Tier)
Combat approach: Balanced combat style. Key equipment: Real Knife Primary mechanic: Route tracking across a whole run
No Hit Challenge Run offers a solid combat experience. Full setup in our builds guide.
Advanced Combat Techniques
Damage Optimization
- Match your equipment to your build's stat priorities
- Exploit Bullet dodging in the SOUL box for maximum damage windows
- Chain FIGHT, ACT, ITEM and MERCY and LOVE, EXP and LV for combo damage
- Use Coloured SOUL modes to create openings
Survivability
- Learn enemy patterns before committing to attacks
- Use Check on every new enemy before anything else. The flavour text points at the ACT option that will spare it, and it costs one turn you were going to spend dodging anyway.
- Position using Bullet dodging in the SOUL box to control spacing
- Save defensive options for guaranteed survival, not comfort
Boss Combat
Bosses test your understanding of every mechanic. See our boss guide for fight-specific strategies.
- Phase awareness: Most bosses change behavior at health thresholds
- Patience over aggression: One extra hit per opening beats dying to greed
- Build preparation: Swap gear and equipment for specific fights when needed
Common Combat Mistakes
- Button mashing: Committed attacks have recovery frames. Mashing locks you into animations.
- Ignoring FIGHT, ACT, ITEM and MERCY: This mechanic exists for a reason. Players who use it take significantly less damage.
- Wrong equipment for the situation: Check our weapons guide for situational picks.
- Not learning from deaths: Every death teaches something. If you don't know why you died, you'll die the same way again.
- Overcommitting: Trading hits works in The Ruins but will get you killed in The CORE.
More Undertale Guides
- Undertale Undertale Overview
- Undertale Best Builds
- Undertale Tier List
- Undertale Walkthrough
- Undertale Beginner's Guide
- Undertale Tips & Tricks
- Undertale Weapons Guide
- Undertale Boss Guide
- Undertale Maps & Locations
- Undertale Crafting Guide
- Undertale Classes & Characters
Similar Games
If you enjoy Undertale, check out these related guides:
- Elden Ring Combat Guide: rpg game with similar mechanics
- Baldur's Gate 3 Combat Guide: rpg game with similar mechanics
- Cyberpunk 2077 Combat Guide: rpg game with similar mechanics
