How to unlock the Fuse Machine
Do Rebirth 1 — it costs $1M Cash and one Horse pet. The machine stands to the left of the “Ride Pet with Friends” board, next to the flying Phoenix near spawn. It is a limited-time feature, so use it while it is in the game.
How fusing works
Put in four pets of Legendary rarity or higher and pay the Cash cost shown at the bottom of the fusion menu (it depends on the pets you use). You get one of 16 Fused Pets. Traits and mutations on the pets you put in have a chance to carry over to the result.
Best Ride A Pet fused pets
The Hydra is the one most players chase; Black Panther, El Toro and Stone Golem are other popular results. Collect plenty of Legendary pets first — every fusion uses up four.