This riftwalker spell damages an enemy over time and can potentially heal a rift entity. If this spell has a use, it hasn’t been divulged by the person who has discovered it. As far as I’m concerned it does too little damage for WAY too many spell points and depends on standing toe-to-toe with monsters for too long a period of time. It gains no benefit from quick chant or quick lips and consumes rift sparks to cast and to power its incredibly disappointing critical effect.

The in game help reads:

No saving throw.
Casting time: 2 rounds.
Damage type: cold.
Type of spell: attack spell.
Affecting stats: int.
Cast type: rift.
Spell point cost: 52.
With this spell, a competent riftwalker can create and control a rift which
shadows an opponents body, leeching life energy into the dimensional rift. The
rift shadow will increase in power the longer it is in existence. A true
master of all types of rift entity can cause huge amounts of damage with this
spell. There is also a chance that critical amounts of energy will be leeched
from the target, some of which will be absorbed by the riftwalkers entity if
they have completed 'The Grind'. Criticals consume a rift spark.
This spell uses 2 rift sparks.