Power Leech

7th-level necromancy
Casting Time: 1 action
Range: 60 ft
Components: V, S
Duration: Concentration, up to 1 minute
Book of Vile Darkness

You create a conduit of energy between you and a target in range. Each round, you choose an ability. The target makes a saving throw for that ability or that  score decreases by 1 for the them and increases by 1 for you. This spell ends if you or the target end your turns more than 60 ft away from each other. The target makes saves at disadvantage if you are within 30 ft of each other. Any ability score changes last for up to one hour and then return to normal.

Power Leech

5th level Corrupt necromancy spell.
Casting time 1 action.
120 ft. range.
Components V, S.
Duration 1 minute. 
Book of Vile Darkness

The caster creates a conduit of evil energy between himself and another creature that fails a WIS save. Through the conduit, the caster can leech off ability score points at the rate of 1 point per round. The other creature takes 1 point of drain from an ability score of the caster's choosing, and the caster gains a +1 enhancement bonus to the same ability score per point drained during the casting of this spell. In other words, all points drained during this spell stack with each other to determine the enhancement bonus, but they don't stack with other castings of power leech or with other enhancement bonuses. The enhancement bonus lasts for one hour after the spell ends.

Corruption Cost: 1 WIS drain

Any spellcaster that prepares spells can learn these spells. Each spell list has an alignment attached to it. If a creature of a different alignment casts one of these powerful spells, their alignment shifts towards the alignment of the spell by one step. Each spell has a corruption cost that is paid when the duration of the spell ends or according to the spell’s description. If the cost is ability damage, it is restored when the caster finishes a long rest. If the cost is ability drain, it does not recover until the creature receives attention from a Greater Restoration spell.