Use Omni Stones in Evomon by opening the Evomon menu , selecting the monster you want to upgrade or evolve, and checking the requirements first. In the current guides, Omni Stones appear as a rare boss reward, and the evolution flow also needs the correct level plus any other required stones depending on the monster.

How to use them

  1. Open the animal-head Evomon icon in the upper-right corner of the screen.
  1. Pick the Evomon you want to evolve.
  1. Press Evolve in the bottom-right corner.
  1. Make sure you have the required stones and level before confirming.

Where Omni Stones come from

The clearest public info says Omni Stones can drop from the World Boss in Main City, alongside rewards like Evolution Stones, EXP Fruits, and Advanced Balls. The same boss guide says players can enter the Boss Zone from the World Boss building in Main City and fight solo or with a small group.

Practical tip

If you are farming for them, focus on the World Boss rewards rather than normal stone farming, since Omni Stones are listed as a rare reward from that activity. For regular evolution stones, players usually farm the Exchange Shop and island bosses, but that is separate from Omni Stones.

Quick note

Public guides I found explain how to get Omni Stones, but they do not clearly show a separate “use Omni Stone” button; they seem to be used as part of the evolution requirements inside the Evomon menu.