Speck absorbs magic, so it can become a pain if you don't kill it quick. Use AtmaWeapon to get past its defenses.
It does not attack, instead, it absorbs magical attacks due to it having inherent Runic. Its primary purpose is to stall the party's attacks while Air Force countdown to unleash Wave Cannon, which deals heavy Lightning-elemental damage to the party.
The fastest way to destroy the Bit is to use Edgar's Drill, Sabin's Raging Fist, Cyan's Fang, or have any character attack with the Ultima Weapon. All of these ignore the Bit's high defenses and will do full damage, likely killing it in a single hit due to its low HP. If the Bit is still alive when Air Force finishes charging Wave Cannon, it will be destroyed so Wave Cannon will not be absorbed.
Bit is notably one of the few enemies in the game with absolutely no AI script - aside from absorbing magic it does nothing in battle.