Invisible Chest Buster, Hand of Them

This spells name is too long to keep repeating, but you know what I mean when I say "This spell"

Summary
This spell is a very high level transmorphing spell that can only be cast by very high level mages, such as Merlin or Morgan. This is shown when Rex Malibu attempts to cast the spell and destroys his own chest, taking one of his feathers. The spell creates a growth in the chest of the target that forms into an arm under complete control of the caster. The growth emerging does no damage to the body, and attacks to the arm cannot be felt, but blows from the arm can hurt the targets body, and if the arm bleeds, blood will leave the targets body. The arm is several times stronger than a human arm, being able to easily smash through thick castle walls when Morgan used it on one of her soldiers. Sustaining more than a few arms at a time is very hard, and the arms will fade away harmlessly if not fed enough magical energy.

Uses
The arm created can be used to strangle, hit, stab or disarm the target when it is stuck to their chest. Merlin uses it in conjunction with Reflective Overlap to equip his familiars with the arms, making them much stronger.