Oxygen Not Included is Klei Entertainment's colony survival sim where you manage a group of Duplicants trapped inside a procedurally generated asteroid. Every breath of oxygen, calorie of food, and degree of temperature must be meticulously managed through complex piping, ventilation, and power systems. The Spaced Out! DLC adds multi-asteroid colonies and interplanetary rocket logistics. With hundreds of hours of depth in thermodynamics, gas physics, and liquid mechanics, ONI rewards systems-thinking players who enjoy solving cascading engineering puzzles.
Boss fights are where Oxygen Not Included tests everything you've learned. This guide covers strategies for bosses across all areas, organized by progression order. For general combat techniques, see our combat guide.
Boss Difficulty Overview
| Area | Difficulty | Recommended Build | Key Equipment |
|---|---|---|---|
| Starting Biome | Easy | Farmer | SPOM System |
| Caustic Biome | Moderate | Farmer | SPOM System |
| Frozen Biome | Hard | Researcher | Electrolyzer |
| Oil Biome | Very Hard | Researcher | Electrolyzer |
| Space Surface | Extreme | Researcher | Electrolyzer |
Starting Biome Bosses
Area difficulty: Easy Recommended level: Cycles 1-50 Recommended build: Farmer with SPOM System
Strategy
The first bosses teach core combat mechanics. Focus on learning patterns rather than dealing damage. Gases in ONI have realistic density — oxygen sinks below hydrogen, carbon dioxide pools at the bottom, and chlorine settles above CO2 — this is your primary tool here.
Key tips:
- Don't rush. Learn the attack patterns first.
- Use gas management to create safe windows.
- SPOM System is enough to handle everything here.
Caustic Biome Bosses
Area difficulty: Moderate Recommended level: Cycles 30-80 Recommended build: Farmer with SPOM System
Strategy
Early game bosses test your understanding of pipe systems. Players who skipped learning this mechanic will hit a wall here.
Key tips:
- pipe systems is critical for these fights.
- Farm SPOM System upgrades if you're struggling.
- Consider switching to Farmer if your current setup isn't working.
Frozen Biome Bosses
Area difficulty: Hard Recommended level: Cycles 40-100 Recommended build: Researcher with Electrolyzer
Strategy
Mid-game bosses are the major skill check. They combine multiple mechanics and punish players who rely on a single strategy.
Key tips:
- You need both gas management and duplicant skills mastery.
- Electrolyzer makes a significant difference — get it before attempting these.
- See our combat guide for advanced techniques.
Oil Biome Bosses
Area difficulty: Very Hard Recommended level: Cycles 80-150 Recommended build: Researcher with Electrolyzer
Strategy
Late-game bosses are serious challenges. Build optimization matters as much as mechanical skill.
Key tips:
- Make sure your build is fully optimized.
- Electrolyzer at max upgrade is recommended.
- Study each boss's attack patterns — most have 2-3 phases.
Space Surface Bosses
Area difficulty: Extreme Recommended level: Cycles 150+ Recommended build: Researcher with Electrolyzer
Strategy
Endgame bosses are the ultimate test. They require mastery of all combat systems and an optimized build.
Key tips:
- Top-tier build with best-in-slot gear is mandatory.
- Master every mechanic — see our combat guide.
- These fights reward patience and pattern recognition above all else.
General Boss Tips
- Learn before you fight — Spend your first attempt observing attack patterns. Don't try to win on attempt one.
- Match your build — Some bosses favor certain builds over others. Don't be afraid to switch.
- Upgrade your equipment — A max-upgraded Electrolyzer trivializes fights that seem impossible with weaker gear.
- Use gas management — The core combat mechanic is your best defensive tool in every boss fight.
- Check the walkthrough — Our walkthrough tells you when you're ready for each boss.
More Oxygen Not Included Guides
- Oxygen Not Included Oxygen Not Included Overview
- Oxygen Not Included Best Builds
- Oxygen Not Included Tier List
- Oxygen Not Included Walkthrough
- Oxygen Not Included Beginner's Guide
- Oxygen Not Included Tips & Tricks
- Oxygen Not Included Weapons Guide
- Oxygen Not Included Combat Guide
- Oxygen Not Included Maps & Locations
- Oxygen Not Included Crafting Guide
- Oxygen Not Included Classes & Characters
Similar Games
If you enjoy Oxygen Not Included, check out these related guides:
- Stardew Valley Boss Guide — simulation game with similar mechanics
- Satisfactory Boss Guide — simulation game with similar mechanics
- The Sims 4 Boss Guide — simulation game with similar mechanics
