This reminds me of an artifact I made on a whim for 2e. It was a spear carved from Szoreny-wood and engraved with runes from Elloge. Each time you scored a hit, your opponent lost a dot in one of his attributes of your choice until the end of the scene, to a minimum of 1.
How might this translate to 3e?
That would presumably translate very well into Evocations.
Shining Ice Razor, an Artifact 3 Blue Jade Reaper Daiklave, actually does something similar.
One of it's basic charms,
Cold Moon Slash (simple, costs 6m, 2i, 1wp) causes any successful withering or decisive attack to apply a -2 penalty to the opponents mobility and feats of strength for the rest of the scene. (Hitting with it refunds the Willpower).
An Essence 3 Sapphire Evocation enhances it.
Heart-Freezing Crescent makes the enemy lose 1 Initiative each turn per such -2 penalty they suffer from.
So, that's not direct penalties to Ability Scores, which would essentially be broader penalties. But turning it into a Simple Evocation that applies such a penalty seems like a good start. You could make it Decisive-only, then it'd seem pretty balanced to replace that -2 mobility/feat of Strength with -1 Strength or -1 Dexterity for the rest of the scene. Or just a Strength-drain seems fine too - that's effectively -1 to withering damage, which is no big deal.
So here's some things:
Silver-Thorn Malfeasance:
Cost: 4m, 2i
Mins: Essence 1
Type: Supplemental
Keywords: Stackable, Uniform
Duration: Instant
The wielder lets Silver Thorn strike where it wants most, at the vital strength of its foes. In addition to inflicting the normal damage of a withering or decisive attack, any foe struck by Silver-Thorn Malfeance feels drained. For the rest of the scene, the victim has their Strength lowered by 1 for all purposes except meeting the prerequisites of charms*. This effect stacks with itself, but can not lower an opponents Strength below 1. Drained attribute points are stored within Silver Thorn for the rest of the scene and can be used by it's other charms.
*needed because otherwise it just feels too powerful against Lunars and Alchemicals. Also, since it's just Strength-Drain for now, the charm is supplemental instead of Simple which does have it's advantages.
Silver Sphere Defense
Cost: 3m
Mins: Essence 1
Type: Reflexive
Keywords: Counterattack
Duration: Instant
The wielders anima into a silver sphere that reflects the deeds of an attacker at the world. This evocation creates a withering counterattack that can hit one enemy within close range for each stored attribute point spent.
Heart-Marring Silver
Cost: (2m)
Mins: Essence 2
Type: Permament
Keywords: Stackable
Duration: Permanent
Prerequisites: Silver-Thorn Malfeasance, Silver Sphere Defense
Silver Thorn can strike all aspects of a being, including its abilities to sustain itself. Whenever she strikes a foe with Silver-Thorn Malfeasance, the wielder can pay an additional two motes to also drain a point of Stamina in addition to the Strength.
Word of Thorns
Cost: 4m
Mins: Essence 2
Type: Reflexive
Keywords: Stackable
Duration: One Scene
Words can sting and bury deep within ones foes. At the cost of two motes and one stored attribute point, the wielder of Silver Thorn can grow a viscous hedge of thorns. These cover the area around him up to short range and takes any shape the wielder desires, allowing for open passages through it. The hedge is an environmental hazard that does 4L damage to anyone who is moving through it (unless they are using an open passage as designated by the wielder) with a difficulty of 5. The wielder is immune to the damage from the hedge and can at any time spend a stored attribute point to re-shape the hedge or make it move up to one range band. The hedge withers into nothingness at the end of the scene.
Expression-Draining Word
Cost: (2i)
Mins: Essence 3
Type: Permament
Keywords: Stackable
Duration: Permanent
Prerequisites: Heart-Marring Silver, Word of Thorns
The wielder of Silver Thorn speaks one of the words written on its blade and curses their opponent with an inability to communicate with the world. Whenever a foe is struck with Silver-Thorn Malfeasance, the wielder can pay an extra two points of Initiative to also drain a point of Dexterity from the foe. The foe also loses the ability to speak one language for the rest of the scene. This language is stored within Silver Thorn like a drained attribute point.
Just the basic evocation-tree of
Silver Thorn (or whatever you want to name it), you could add in additional ways to use stored attribute points, maybe control that hedge directly or do other such things.