Devaluing is the inevitable second stage of the cycle of narcissistic abuse. This is where the idealization and love bombing end, and the criticisms, belittling, and neglect begin.
Narcissists hold their victims to unrealistic standards. Only perfection on your part can possibly reflect back to them their own imagined perfection. Should you fail in this mission—and you will—you'll be met with a barrage of criticisms, nitpicking, fault-finding, coldness, indifference, and other forms of invalidation. The person who initially showered you with attention, affection, and approval is nowhere to be seen; Nice Dr. Jekyll has morphed into mean Mr. Hyde.
This shift in behavior is often gradual, sneaking up on you as you wonder what you've done to deserve this newly demeaning and degrading treatment. You're left reeling in confusion, feeling unsure of yourself, anxious, depressed, full of self-doubt, and unworthy of love. This is exactly what the narcissist intends. Narcissists, you see, have a "man up/man down" mentality. Which means if you're down, they're up.
If you're in a relationship with a narcissist, you will always be "man down." While the narcissist may cycle back through the love bombing stage to a degree if they sense you pulling away, just know that once they feel secure again, more devaluing is around the corner. With a narcissist, it's inevitable. And predictable.