The Sinscale is an enemy encountered in the opening portions of Final Fantasy X and is the first enemy the player encounters. It is a fiend that falls off of Sin's shell, yet retains its own intelligence.
The Sinscale is a basic enemy that fights with only a simple physical attack, but may sometimes perform a move called Charging Up which, on its next turn, will unleash an ability called Spines. One or two physical attacks should be enough to take one of these creatures down.
When Sin attacks Dream Zanarkand, Tidus and Auron attempt to reach Sin by fighting off a horde of Sinscales. Sinscales come in the blue-green variety, and a variety that has violet eyes. When waterlogged, Sinscales remain in their closed scale form and flex their bodies to swim. Swimming Sinscales can only perform an elementary tackle attack.
The second incarnation of the Sinscale is encountered when Sin attacks the boat S.S. Liki near the beginning of the game. The only difference between this variety of Sinscale and the type found in Zanarkand at the start of the game is higher HP and higher Strength and Agility levels. This variety also drops items and can be stolen from (unlike the first incarnation).
Notably, if one can kill them in one hit, they are an excellent source of AP and Power Spheres early on in the game, and with patience, the player can obtain the Overdrive Modes Warrior and Slayer for Tidus, Wakka and Kimahri. For this, Tidus should use Cheer a few times until the party can kill them in one hit.
The final incarnation of the Sinscale encountered in Final Fantasy X is only encountered in the battle with Sinspawn Echuilles underneath the S.S. Liki. Tactics remain the same as with other Sinscales, but only Tidus and Wakka participate in this battle.