FFX - Sidequests - Village of the Cactaurs
After you gain control of the airship go back to Sanubia Desert. There is a large rock deep in the desert with a picture of a cactaur on it. Each time you examine it you will be told a clue to find each of the 10 cactaurs hidden in the desert. After finding one you will play a game along the lines of "red light/green light".If you touch the cactaur before time runs out you'll fight him. If you win or lose the battle you'll get a sphere with the name of that cactaur on it. If you lose the red light/green light you will get a Sphere del Perdedor. No matter what you get go back to the stone and put whatever sphere into it. You will receive a clue after doing so to find the next cactaur. Follow the same procedure to find the rest of the cactaurs...
Oasis
Near the first save point.
Sanubia Desert - East
In the alcove to the east, north of the tent with the save point.
Sanubia Desert - West
Search the 20% off sign near the Cactaur rock.
Sanubia Desert - Central
Near the ruins to the west. Look for two cactaurs running around.
Sanubia Desert - East
Near the save point under the tent.
Sanubia Desert - West
Trapped in a treasure chest in the far west.
Sanubia Desert - Central
Inside one of the whirlpools in the sand.
Oasis
Teleport back to the airship and go onto the outside deck.
Sanubia Desert
Return to the Cactuar rock and the last one is there.
Once you put 9 spheres into the rock the sandstorm protecting Cactaur Village will stop. Here you will find two treasure chests. One contains the Mercury Sigil the other a rare item.