That's still only 14, which is sort of, well... pathetic. Let's make it 18 for starters.
I'm going to go out on a limb here and say that these'll have a lower CR than an ordinary beholder?
I'd expect, though a "death cone" from the central eye isn't bad.
Special Attacks: Deathcharm eye
Combat: The beholder-mummies’ main form of attack is their central eye. It retains the range it had when alive, but the eye now bas a two-pronged attack. The eye acts as a powerful charm monster to those characters or creatures who are affected by such spells; to those who are not, it acts as an equally powerful ray of death magic.
Any who encounter the kasrharin make their saving throws at -4. If they can be charmed and fall their first saving throw, they continue to make all successive saving throws to shake off the charm at -4 as well. Creatures and characters that cannot be charmed because of inner magic resistance or immunity must make a saving throw versus death magic at -4, with failure indicating immediate death.

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