The creature's flowing sand form allows the Sand Devil to avoid taking any serious damage, the player must have a Water Tome or three Antarctic Winds in a one character's inventory. Using Water or an Antarctic Wind, causes the Sand Devil's flowing sand to harden and allowing more damage to be dealt for two turns.
During the time the monster's sand is hardened, constantly use physical attacks. When the Sand Devil's health begins to deplete, it will begin to cast Sandstorm, so have Cure ready to heal any seriously damaged party members. After two turns of physical attacks, the Sand Devil's sand will begin to flow again, so the player should use Water or the Antarctic Wind again and repeat the same strategy. After a couple of turns repeating the same strategy, the Sand Devil should eventually fall.
The Sand Devil in the Moonsand Ruins acts twice per round and uses physical attacks that may petrify the target, so the player should have Esuna in their inventory. The strategy used during the previous battle still works, but players should use higher level spells such as Waterga or Blizzaga instead. During this time, the player should use Finale and physical attacks to deal major damage to the monster. When the Sand Devil's health begins to deplete to 50%, it will begin to cast Sandstorm, so the player should have Curaga ready to heal minor injuries. After a couple of turns repeating the same strategy, the Sand Devil will eventually fall.