A full pen is the wall most Steal an Egg players hit long before they run out of eggs to steal. Duplicate pets pile up, every slot is spoken for, and there is nowhere to put the next hatch. The Fuse Machine is the release valve, and it does something more interesting than simply deleting spares: it hands back an egg whose size is rolled fresh, which is where the occasional 500,000kg monster comes from.
Quick answer: Carry three copies of the exact same pet to the Fuse Machine, drop them into the three slots, and pay the cash fee. The three pets are consumed and you get one egg of that same species, with its weight re-rolled — it can come out heavier than everything you put in, or lighter than any single input.
Fuse Machine requirements in Steal an Egg
The machine sits at your own base, near the pen, and there is no unlock step or cooldown attached to it. The only real gate is having three of the same creature at once, which does not happen early on because new biomes keep handing you new species faster than repeats build up.
| Requirement | Detail |
|---|---|
| Inputs | Three pets, all the exact same species |
| Mixing species | Not accepted in any combination |
| Cost | In-game cash fee that scales with the inputs |
| Location | Fuse Machine at your base |
| Cooldown | None — usable back to back |
| Output | One egg of the same species, weight re-rolled |
The fee is the part people underestimate. A triple-Scorpion fusion has shown a $114M charge, while late-game species run into the tens or hundreds of billions. Cosmic Dragon fusions have been logged anywhere from $35B up to $757B, and Stag fusions in the $59B to $238B range. That money is competing directly with your treadmill and base upgrades, so it is worth checking the number on screen before you commit.
How to fuse three pets and hatch the result
You know it worked when the three inputs vanish from your inventory in the same moment the new egg appears. Nothing is recoverable after that point, so the check has to happen before you press Fuse, not after.
The weight re-roll: why fused eggs can be enormous or tiny
This is the mechanic that gets misread. Heavy pets going in do not add up to a heavier pet coming out. The egg gets a fresh size roll, and the in-game text only hints that better pets bring “more luck” — there is no published formula, no floor, and no odds. Recorded fusions land all over the map.
| Inputs | Fee | Result |
|---|---|---|
| 3 Scorpions (457 + 256 + 247 kg) | $114M | 86kg Scorpion — lighter than every input |
| 3 Silver Yetis | $9B | A larger Yeti egg, modest gain |
| 3 Brontos, mixed sizes | $13B | Average Bronto egg, no visible gain |
| 3 Cosmic Dragons (~40–43k kg each) | $108B | 49,000kg Cosmic egg — bigger than any input |
| 3 Eternal Lunar Dragons | $94B | Heavy egg that hatched well |
The upside is real when it hits. Fusing duplicate Secret, Cosmic and Eternal pets has produced a 10,481kg Cherry Blossom Egg, a 515,632kg Cosmic Egg, a 200,438kg Prehistoric Egg, and a community-recorded Cosmic Egg at 4,052,770kg. Those numbers are outliers, not expectations, and 960kg of Scorpions turning into 86kg is the same machine on a bad day.
Note: Treat every fuse as a re-roll with a free slot attached, not as an upgrade button. The guaranteed part is the inventory space; the size is a coin flip.
What a batch of fused eggs pays out
Clearing a backlog in one sitting is where fusing earns its keep. Working through duplicate Stags, Cosmic Dragons, Cosmic Skeletons, Cerberuses, Lava Dragons, Phoenixes, Mosasauruses, Mutant Sharks and Lunar Dragons empties a pen fast, and every one of those fuses is another shot at a heavy egg.
One full clear-out and instant hatch produced a 1.7B/s Stag at 13,150kg and a 2.2B/s Silver Gorilla King, both of which replaced existing pets outright, plus a 1.1B/s Silver Eternal Lunar Dragon and a 516M/s Golden Cosmic Dragon. Two team upgrades out of a batch is a good session, not a typical one.
Mutations and fusing: what you can lose
Mutated pets carry income multipliers, and the machine does not protect them. Feeding one mutated copy in alongside two plain ones is the fastest way to delete a multiplier permanently — a captured fusion that included a Silver Scorpion did not visibly preserve the Silver on the output.
The only pattern worth attempting is three pets that all share the identical mutation, which is reported to keep that mutation on the result with a chance at a larger body. Anything with a Rainbow, Bloom or Spirit Bloom roll should stay out of the machine unless you own two more copies with the exact same mutation and can afford to lose all three.
When to fuse and when to leave pets in the pen
Every pet placed in your base earns money per second. Fusing removes three earners and gives you one, so the maths only works if the replacement plus the freed slots beat what you had. Check your total money per second before and after — it takes seconds and stops the most common income drop.
| Situation | Fuse it? |
|---|---|
| Three low-income duplicates you have outgrown | Yes — clears clutter for one re-roll |
| Three copies that are your top earners | No — they earn more left in place |
| A pet with a rare size or mutation | No, unless all three share that mutation |
| Spare Secret, Cosmic or Eternal duplicates | Yes — best odds at a genuinely huge egg |
| Pen is full and eggs are waiting to be placed | Yes — space is the guaranteed return |
The rule that keeps collections intact is simple. Keep your strongest copy of every species out of the machine, feed it only true spares, and log the egg weight and money per second after each hatch so you can tell whether a species is worth fusing again. Do that and the Fuse Machine stops being a gamble on your best pets and becomes routine maintenance that occasionally hands you a 500,000kg egg.
