Memory alteration magic sources

I've knotted together a scenario, where I would like a bit of help unraveling.

TL;DR backstory of one of my players is that he was orphaned/abandoned as an infant and now he's looking for his parents (or mother actually, since the party killed his father... or the undead form of his father). Aaaaanyway... Recently, this character got possessed by my homebrew monster who took him to Shadowfell, where he eventually killed the monster. In order to return to the Material Plane, he had to solve a puzzle and in order to solve the puzzle he had to pay a price... a memory. The memory the player chose was that when he was a kid he went to the market with his mother and he wanted some new clothes, which his mother didn't get him (he's also quite a fashion "guru", always crafting clothes for himself). This lead into the situation that the prize to leave Shadowfell was the memories of his mother. He remembers him being at the market with someone, but he has no idea with whom and so on. This slightly contradicts his original backstory of being abandoned as a baby.

They'll soon have an opportunity to meet with a devil, who will very kindly offer to return this character's memories to him. Only for the devil to also realize that it's not the first time the character's mind has been tampered with. A devil won't admit they can't do something, so I need to plan out his roleplay accordingly.

Because of the mismatch between the original backstory and the memory the player chose, I decided that he does indeed remember something of his childhood, but they are affected by some other magic. I don't want to use another Shadowfell creature nor another devil. I thought the mother went to a hag to remove her sense of remorse, so that she can leave the baby and advance her own career. At the same time the hag altered the character's mind, so that he would simply forget to think about his parents. In place, the hag would place alternative memories into his mind to fill out gaps.

Now my question is this: which creatures have this sort of memory alteration magic available for them already? Which type of creature would most likely agree into something like this? Even if it is a ready monster, I will probably homebrew it slightly to fit into the story. I'm preferably looking something like a CR 5-12 monster, so that I don't have to homebrew too heavily. Any suggestions?

Not sure could make it a feat or spell. 

Made this for you Memory alteration

Thanks, but that's not really what I asked.

Sorry

Mind flayers, Aboleths, and Oblexes could all work. Or Amnizus, but they have a higher CR than what you said.