To shoot an arrow when you step on a plate:

- Place an item with the turret script, e.g. the "PUZ_Trap_Gargoyle_C" gargoyle.

- Prefix your pressure plate name with S_ so it becomes e.g. "S_PUZ_PressurePlate_Floor_A_000".

- Open the gargoyle for edit, go to the Scripts section, edit the "PUZZLE_Turret" script, set "TurretShootEvent" to "plateStepOn" and set the "TurretProjectileSkill" to e.g. "Projectile_StunningArrow".

- Set the "TargetItem" to the pressure plate

Then whenever you step on the plate it will shoot at the arrow at it. Don't think you set it to target a player though.