The Crossbow Turret is a crossbow mounted to a swivel. The crossbow turret fires special holy arrows that can harm creatures that have a lot of protection, such as a dragon. However, the arrows fired by the crossbow are somewhat slow and take time to reach a target.
The crossbow turret's arrows take time to reach a target, which can be a problem when fighting Cecil. This can be compensated for by aiming ahead of Cecil so that he collides with the arrow while in mid-air. This takes a little knowledge of how Cecil moves, but when this is mastered, it can be very effective against him, as it lets the player harm him while he's moving and when he's stationary.
The crossbow turret is fragile, as only a few hits from Cecil's fire-breath can destroy it. However, a new one will spawn in another part of the level as soon as it is destroyed.
If the player wants to prevent Cecil from damaging a turret as much as possible for some reason, control and fire a turret while he's away. When he starts moving, jump off the crossbow and start moving away from it. This will prevent Cecil from harming the crossbow, but will put the player in danger of being hit by Cecil directly.
The player is required to collect arrows for this crossbow scattered around the arena. Because it takes multiple shots to kill Cecil, collect multiple arrows before manning a turret, so you won't need to leave to collect more ammunition.