Retaining old parts of themselves means they keep some memories and the strongest aspects of their personality.
They can use magic if they used to be mages but the association usually gives them a mana allowance to use the basic energy attack and shield spell.
Mages can be made into homunculi if killed by a chimera and can use some of their old spells.
Mechanically they are about 80% flesh and blood, with the remaining 20% being enhancement spells.
They are entirely competent, as smart as they were before death and mostly emotionless, with only very minor emotional reactions.
(E.g oh... My friend died...)
They have organs and stuff but are far more durable than the average human, and heal quickly.