Countdown to Midnight

Upon casting this spell, ethereal tendrils form between the caster and their targets, with the caster as the nexus of these tendrils. As long as two linked individuals are on the same plane of existence, the tendril(s) remain.

A tendril is invulnerable to all attacks (magical and non-magical), and can only be removed by casting Dispel Magic where only a single tendril is severed from each casting of Dispel Magic. A tendril is also removed if either linked individuals move into an anti-magic field. 

At the start of each linked individual's turn, starting with the caster of this spell, the individual takes 6d10 necrotic damage or half as much on a successful Constitution save (DC 20 if none are specified by the caster). Furthermore, half of that damage lowers the hit point maximum of the caster's target(s), and lasts until a long rest or a Remove Curse spell is applied to each target. This necrotic damage bypasses any necrotic damage resistances or immunities.

As long as an individual remains tethered, healing from any source is negated (similar to being under the effects of the Chill Touch cantrip). This condition does not apply to the caster of the spell.