@archhexblade1 replied to your post “Spell: Phantasmal Killer”
It's not a sorcerer spell because no creature innate uses spells like that in the forgotten realms (primary source of lore for 5e) so no bloodline can transfer it. If you're running a homebrew setting where that's not the case then why complain at all?
I see four problems with your reply (three with your argument):
You take issue with the act of complaining. You’re going to have a very foul time on my blog; I do that by default. And I’m not going to be remorseful for being that way, nor will I stop because someone asks. Complaining points out where things fall short, thus giving us the ability to grow; it’s why we have nice things.
“My Grandpappy Screwed a Nymph” Fallacy. Despite a common thread going all the way back to 3.0′s introduction of the class, by canon not every (or even most) Sorcerers draw their power from having non-human DNA in their background. Of the official out-of-playtest material, the only one that is de jure heritage is Draconic. The fact of the matter is that sorcery has a lot to do with the unique way each sorcerer approaches magic. It can have to do with inheritance, but it doesn’t have to.
The Homebrew Fallacy. The Forgotten Realms may be the source of much lore, but it’s generally been the case in most editions (I can’t really speak for 4th) that lore is optional (as you indicate by mentioning homebrew settings) and largely flexible, especially in the department of what magical abilities creatures have. Generally, what goes into a Monster Manual doesn’t usually dictate what options are available to players (to the point that it made polymorph an ongoing problem in 3rd edition). Further, saying that you can homebrew it is not an adequate defense of a problem with the rules, even if it is a viable solution to a given problem at hand.
The False Assumption about FR Canon. This one is the pièce de résistance because if your argument were correct, then it would be true for every spell included on the spell list -- so you wouldn’t have specific odd spells like darkvision, false life, jump, water walk, and such. However, you could say that those represent something similar to effects which monsters in the Realms can produce, to which I reply that there are loads of psionic monsters (Aboleths, Illithids, Yuan-Ti, etc.) which have mental assault and/or illusion-based powers, which phantasmal killer replicates handily. Further, it would call for certain other spells not currently on the Sorcerer list (like animate dead¹) to be on the list. But above all, the idea that a canonical monster would have had to have it to be on the Sorcerer list would demand that no monster in the Realms has ever innately cast phantasmal killer. That’s not true. Since I do not yet know of a website with a full, easily searchable list of every monster as yet published in 5e, I had to get a bit...archival. Because the 2nd ed. Monstrous Compendium is online in its entirety, I often go to it in my searches before seeing updated versions. This time, I found the Death Slaad, Minion of Set, and Piscoloth, (I didn’t dig that deeply, either: Google is lovely, if evil), all of which have a presence in the Realms. The Minion of Set worked differently in 2nd ed. than in 3rd (it’s in Deities & Demigods, which I happened to have on hand). You might say that supports retconning as a defense of your argument, which is entirely arbitrary. Regardless, I figured the Minion of Set likely hasn’t gotten updated to 5e, so we’ll need to hold onto that thought for the moment. Since the Piscoloth is in various books, I decided to track down the Death Slaad. (Though it’s in the 3.x Monster Manual, it’s considered Product Identity so isn’t on the SRD; thus, I had to dig out my Monster Manual to check.) It doesn’t have phantasmal killer in 3.5 (no clue about 3.0, not going to dig that deeply). I compared this against the 5e Monster Manual; they don’t have it there, either. I sighed: I would have to search for Piscoloths. This is where I pulled out a trick: I turned to this wonderful website called Forgotten Realms Helps, which catalogs FR material from 3rd edition (and other material, which it then notes is non-Realms stuff). I looked up “Piscoloth.” It has phantasmal killer. Thinking I should check for retcons, I looked at the Forgotten Realms Wiki to see which book Piscoloths appear in now; it doesn’t list them as having yet been published in 5e, even though they were in every numbered edition beforehand. This means one of two things: either they haven’t been published yet (quite plausible) or piscoloths are being retconned out of the setting (but that seems unlikely: why say “these no longer exist” needlessly?).
So, until I can find a nice, tasty, readily searchable repository of literally every published, canonical monster in 5e, again we’re back to until WotC finalizes its psionics origin for Sorcerers, if they ever do, you’ll have to find some other way of getting the spell.
Which goes back to Point #3: homebrew/asking your DM is a viable option (depending on the DM), but not an adequate defense of the rule.
¹ You might argue that that has to do with being a ritualistic spell with a longer casting time, even if you don’t cast it as a ritual. The same is true of teleportation circle, which is on the Sorcerer’s list.