Transfusio

The cantrip facilitates the use of one creature's hit dice to heal another. The caster and a willing donor must remain still until the beginning of the caster's next turn. Unwilling donors must be restrained. An unwilling donor must make a Constitution saving throw or lose one of it's hit dice. At the beginning of the caster's next turn, the recipient may roll the donated hit dice and regain hit points equal to the total. A creature reduced to zero hit dice takes damage equal to one of their hit dice.