Vatlings
As previously stated , sorcerers grow artificial bodies in order to duplicate spells. Typically, very short-lived homunculi are used, lasting just long enough to get the job done. Some sorcerers create longer-lived homunculi via this process however, commonly referred to as vatlings. Here's a system for their creation accompanied by some bad scans of crappy watercolor splotch drawings I made. The demon-flesh samples used to grow vatlings are contained in specially-constructed zinc cylinders that stabilize the tissues for long-term storage. They're expensive to create and feed, so mostly sorcerers make do with a handful of strains, but if a new mutation is particularly useful it can be tempting to add to your repertoire. When finding a new tissue sample (from another sorcerer), roll random characteristics for the fleshy shells that strain creates (or just make something up):