From the Beta Notes:
Is this a secondary ability of Life Cocoon?Death Cocoon
Encases the target in a harmful cocoon of Chi energy, dealing 5 damage every 1 sec and causing any healing recieved to be damage instead.While in the Cocoon, the target moves at -50% reduced speed and is unable to attack or cast spells. 40 yd range, 2 Chi, 2 min cooldown, Instant