Whalesark
A wizardry-powered shadow of a whale's nervous system, into which a temporary deep-level shapechange spell has been woven. Before activation a whalesark manifests as an irregular web or network of greenish-white or bluish-white light, with glowing or flashing spell nodes at the structure's junctions.
Kit is lent a whalesark by S'reee for use during the Song of the Twelve. He is warned to be extremely careful with it, as whalesarks can only be made when a live whale near death (normally a wizard) donates his or her nervous system for this unique purpose. Other wizards use the donor's neurological information to create a spell-powered duplicate of the nerve-mind interface. The assisted shapechange spell which is then wound into the cetacean neural data enables a particularly effective and long-lasting change -- useful for wizards doing prolonged undersea work, where having to deal with the side effects of "lighter" shapechanges would be troublesome. Contact with the sark and the intention to use it is sufficient to trigger the change.
The use of a whalesark itself, however, is not without its dangers, as Kit discovers when he spends too long in the sark. The dead whale's neural data will eventually begin to overwrite both the sark-wearer's neurology and his or her thought processes with shadow data left over from the donor -- at which point the wizard wearing the sark is courting either catastrophic rejection (a bad thing when you're a mile or more down in the water) or irreversible change. (DW)