Because of its liquid state, lich’s blood is immune to all weapon-based attacks. Thanks to its magic-draining nature, all spells cast on it are absorbed harmlessly. The only way to kill a lich’s blood is to use nonmagical acid, fire, or the deprivation of magic. A dispel magic spell cast on lich’s blood causes 1d6 hp damage per level of the caster; an anti-magic shell cast on one destroys the creature immediately.
Sounds good, but sweet Vecna is this thing tough. It's going to have quite the CR.freyar said:How about DR 10/- and Regeneration 5 (fire and acid do normal damage)?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.