The Cross Boomerang is without a doubt the strongest of all sub-weapons in the Castlevania series. It's got a stronger impact than other sub-weapons and can also provide multiple quantities of high damage.
The Grand Cross is the item crash of the Cross Boomerang for Richter Belmont. In Castlevania: Rondo of Blood it's comprised of him being in the air with the sudden appearance of a large cross behind him which damages all enemies which makes physical contact with the cross. While in Castlevania: Symphony of the Night it follows the trail of a beam around him and finishes by flying off the screen inflicting damage on any enemies along the way.
Used by Julius Belmont in Castlevania: Aria of Sorrow and Castlevania: Dawn of Sorrow, this is his personal item crash. One way it's used is just as a Cross Boomerang and the other is through being in the air and forming a cross with his body. It becomes a burning cross, burning with the flames of holy fire, which also has the potential to suck enemies into it.
Circle of Moon:
Symphony of Destruction:
Used by Richter Belmont in Castlevania Resurrection