Obsolescence [ɑb.səˈlɛ.səns] N. The process of becoming obsolete

One night, coming home from delivering a suit to a high-priority customer, Rarity finds her dear sister covered in cuts. The seamstress’ cat just happens to have blood on her claws.
As far as Rarity is concerned, Opalescence is now obsolete, or rather; a living definition of Obsolescence.

But who is truly behind this? It can't honestly be Opal, the sweetest, if not grumpiest cat in Equestria?