What spell would have this effect?

[Inessaria]

Brand new DM here. I've only been playing D&D since August, but needs necessitated I become the DM for a very small group (2 players and myself).

At my first game, the players went completely off the reservation and I had to begin making things up as we went. I ended up with an item, but I did the know what the item was yet, since I had only created it 15 seconds earlier. The players were asking for eyewitness accouts of the item, so I made everyone forget what the item looked like, since I still didn't know.

I now know what the item is and what it does, but I need a spell that would account for no one being able to remember it. I am not well versed with the spells, as I tend to play the klepto rogue type. Both of my players are magic users and one of the is the type to break out the PHB every 5 minutes to verify that's how a spell works. While I have some leeway by being DM, the less fuel I can give him the better.

It may help to know this is set in Faerun at the very beginning of the Time of Troubles, so I could get away withe a spell being corrupted by a Wild Magic Surge, if I had to.

[Coffee_Dragon]

5E operates very much on handwaving and DM invention when it comes to any magical spells, effects and enchantments that are not of the player characters' doing. If you're imagining a +2 thing of mindslipperiness, you can have it working to any desired specifications, and no one can expect to be able to look it up somewhere. Just aim to be as consistent as possible once you decide how it works. If you feel it would have to be too contrived to account for everything that happened before, it shouldn't be that big a deal to tell your players you need to retcon some detail or maybe replay a short exchange with one of the potential witnesses.

If the player breaking out the PHB is trying to catch you with a mistake or gain out-of-character knowledge from the rulebook that's a behaviour I would try to talk him out of. It's a good thing if players keep track of their own spells, but that's not the physics engine the rest of the magical world needs to run on and they shouldn't try to use it as some sort of reference and validation of what they encounter.

[Inessaria]

Since, in this case, the item is a pint sized golem or homunculus slated to carry out an assassination, having it be forgettable seems appropriate. That would also account for the faint magic residue left behind where it was resting for 2 months. I will get used to saying, "It works that way because it does. Either put the book down or roll initiative."

Thank you for your feedback.

[JellyPooga]

Coffee_Dragon has the right of it, but to answer your question directly, Modify Memory is a spell with the capability to do pretty much what you want. If you get to a point where you feel you do have to codify this ability (for whatever reason), then using that spell for guidance and/or inspiration to help balance the effect would be a good place to start.

As a GM, it's important to realise the the Players Handbook is for players. Only PC's are constrained to any of its contents. As GM, it is your prerogative, privilage and right to "make it up"...if that means breaking the rules the players play by to tell a better story, then so be it. Just don't let the power go to your head!:smallwink:

[Daishain]

As the DM, you are not constrained to the spells in the official books.

In fact, you should be aware that those spells are only a tiny fraction of the spells that can be cast, and just represent some of the more commonly known ones. You are perfectly free to modify how spells work, and even make up entirely new ones, and your players have no grounds with which to object.

Now, in the interest of game fairness, I suggest avoiding freely screwing around with spells flung at the party in combat, and also to avoid creating spells that would be considered broken by comparison to other spells of the same resource expenditure. (In fact unless the creator is a master spellcrafter, I tend to make my custom spells a little underpowered on that scale, with the thought that the common ones are often more efficient and thus favored for a reason). But aside from those guidelines, do what you will.

Similar provisions exist for magic items. The stuff found in the DMG is a tiny droplet in the lake of potential enchantments. With this in mind, it doesn't need to be a spell effect that made them forget. An object that erases itself from the minds of others is entirely within your bounds.

And thus, I present to you, your magic item:

The Casket of Forgetfulness
Wondrous item

Originally created to protect objects deemed too dangerous to allow free access, and too difficult to simply destroy, these caskets are designed to erase their existence from the minds of those who perceive them. A DC 25 Wisdom save allows an individual to perceive the casket as it truly is. A DC 15 Wisdom save allows an individual to perceive that something has happened to their memory and perception, if not exactly what. Failure leads an individual to be unable to recognize the existence of the casket, even if its presence would normally be quite obvious. The save is repeated once a day while the casket remains in a person's vicinity, with individuals who previously recognized the box losing all memory of it if they fail.
As a second line of defense, most caskets are also fitted with sturdy locks (DC 25 if the picker cannot see what they're doing, DC 15 if they can)

Just assume that last time, enough of the party passed the DC 15 mark to recognize something was there, but none hit the DC 25 mark. Your party will probably have difficulty opening the casket, but that's rather the point. If they utterly fail, let them do research on the thing and have hints pointing them towards a significant plot item in your campaign. And thus your problem item becomes an important plot hook!

If the party does succeed in opening it, roll a d6. On a 1, the box is empty, on a 2, the box contains a selection of valuable items (the property of a strong willed individual who wanted extra security), on a 3, the box contains an imprisoned creature, such as one of the genie types, on a 4-6, the box contains a dangerously cursed magic item of your choice.