Gosh, Twiceborn only affect the caster...so I need cast Gift of Reason on the Clam first and then empower it in Death Magic before it can cast Twiceborn on itself, which will only yield a standard wight mage as with everything else...
(I like the idea of the disease and nausea spreading undead clam! Useless Unholy gems are not so useless: Collect many of them and send them to your enemies, so that it will flood their labs - aint there a maximum gem capacity as for items in the lab?)