Crown Undertaker is a Noble Phantasm used by Darius Ainsworth through a Nameless Class Card. It launches a number of thorny vines that proceed to encircle and trap the target in a spherical barrier. Illyasviel von Einzbern is able to easily destroy it with a swing of Excalibur from the Saber Class Card. Julian also manifests thorns during his ritual to produce the tablets from Miyu's blood, but it is unknown if they are related abilities.
The Noble Phantasm is exclusive to the anime adaptation of Fate/kaleid liner PRISMA☆ILLYA 3rei.