What you are looking for is Involuntary Transformation. It's a Drawback from page 126 of the Core rulebook.

Involuntary Transformation

You have two or more forms or identities you sometimes change between against your will. The value of the drawback is based on how often you change (frequency) and how difficult it is for you to resist the change (intensity). If you cannot resist the change, no matter what, the intensity value is 3 points. If you involuntarily switch between super-powered and normal human forms, you also have the Normal Identity drawback.

Remember that Drawbacks vary in their point values depending on frequency and intensity and the details should be worked out with your GM.

This is evidence of a dysfunctional gaming group, if these actions and arguments are typical.

Hi, Fincam. I recognize you're new here, and I am aiming for 'stringent' rather than 'harsh.' I sincerely apologize if I miss the mark.

But that said, I think you have a larger problem than you think.

I see not one, not two, but three people with varying levels and types of culpability. But before that, a preface: There are no formal rules for treasure division in 5e as far as I know. Nor are there formal rules for how a GM should insert him or herself into that process. These are matters rightly left to the domain of roleplaying, in my opinion. Therefore, so is this answer.

But one can definitely form an opinion about the roleplaying choices and GMing choices being made, which can and do influence the suggested course of action that will come at the end of this post.

Now then.

First, you: Yes, you were instrumental in finding the Sentient Sunblade. But by your own word the (apparently informal) rules of treasure division in your group are:

Generally in our group, we give the loot to whoever is better able to use it, otherwise is finders-keepers unless he/she wants to give up the loot. The sword was a special case because there was a 5-way argument between all of our potential sword users over who got it.

I'm not sure what the special case here was that led to your character's claim over it, though, since your character (again, your words) lacked the proficiency to use it effectively. The special case here, to be blunt, seems to be, "You really really wanted the sword."

So your character kept it. Apparently by fiat and apparently over the objections of the other characters and players. But more than just keeping it, you also decided you were going to loan it out on a session-by-session judgement, role-playing it as though this were an act of generosity on your part.

I've seen treasure disputes, some that seemed justified, some that didn't. I've never seen someone keep an object they could use sub-optimally at best only to loan it out every session. It reminds me more than anything else of PC clerics charging for healing spells. If I were a player on the receiving end of this, I would be very concerned that the sword would be 'awarded' to whoever did you the most recent big favor.

I am not saying that you personally had this scheme in mind, or that you would have done this. But this would definitely be on my mind and would definitely be unpalatable.

This is an example of a questionable role-playing choice with a clear and foreseeable consequence of annoying one's fellow players. This sort of thing (constant squabbling over treasure, or my example of charging for healing) are in my experience very well correlated with "My Guy Syndrome" on a player basis, or just dysfunctional groups in general.

Second, Vanessa: Even so, stealing the sword is arguably poor form even if done in character (although as an in-character response to another character in-character hogging an artifact... maybe not as poor form as it otherwise would be.) Stealing the sword outside the rules, however, is an escalation into just plain cheating.

Outside the context of the prior actions, I would have simply not acknowledged the theft unless and until I had heard the GM tell me it happened. With that context, I would have taken it as a sign of just how deep feelings were running.

Third, the GM: It's not entirely clear to me how Vanessa managed to steal the sword. It sounds like she simply declared it and the GM either acquiesced, or that it never came to the GM's attention in the first place. Regardless, as a GM, this is easy to stop by saying, "No, sorry, that did not happen. The possession of the sword is unchanged."

The punishment of the cursed amulet is also highly questionable because it is indirect and ad hoc, after the fashion of Gygax's "blue bolts" and "ethereal mummies." If the player were not complaining about it being a punishment, I would question whether the two incidents were linked at all.

But prior to that, during the original dispute, I would pointed out to all of you that what you are all arguing about is not a what but a who! The DMG says clearly on p214 that sentient magic items are NPCs in every meaningful way-- they are self-aware, have likes and dislikes, bonds (which may include goals) etc.

• You are all arguing over possession of a sentient being.
• You are loaning out a sentient being for use by others.
• Vanessa stole a sentient being which your character had claimed possession of.

Some of those might be waved away as out-of-character, player level discussions. Yours cannot. Vanessa's cannot.

The least I would have done in the moment is have the sword point this out to the group at large during the original dispute (and frankly, it might not want to work with any of you.) I'd also rule on-the-spot that the sword requires attunement in order to prevent it being passed back and forth.

So here is how I would deal with the situation:

First, the gambling situation: There's not quite enough context to make a hard judgement call. In my mind, the question would be one of stakes: Were you all gambling serious and/or unique stakes? If yes, my sympathy would be with you, as you stood to lose something precious. If no, I would be inclined to treat your really good roll the same as the Paladin getting a critical hit in combat, which is to say, as a part of the group effort.

And in either case, I would advise standing aside on this one because no matter what you say about the sun blade not being a current issue, it is clearly a current issue in Vanessa's mind. Good gaming often requires you to take seriously the thoughts and feelings of your fellow players.

But that's not your real problem. Therefore...

Second, the longer term situation: You guys really need to address the long term problems affecting your game. And from here, they look like multiple examples of poor sportsmanship-- squabbling over treasure, grudge-holding, out-of-character cheating (or a remarkably inattentive GM) and bad GM calls.

You guys really need to sit down and work your way around to two things.

First, figure out for once and for all, how you're going to divide treasure, and in what circumstances it is applicable. I get it, it's not easy. Magic items are big, unevenly priced parcels with different utilities for each character. I've studied problems like these formally, and they are vicious. Solutions in the past that have worked for my groups include:

• Converting the items to GP value and requiring the receiving character "pay" for them on possession. This tends to keep the same players from getting all the items because they run out of funds. This requires a little help from the GM, in terms of keeping the characters solvent enough that this works.

• A second price ("Vickrey") auction, and then as above. This mostly solves the solvency problem since the players are setting the price.

• Irreconcilable disputes are settled by selling the item and distributing the value evenly. This requires the GM to run a game where such objects are readily salable.

I have seen other groups come up with rotating schemes about who gets first choice on any given haul, but I have never made it work in any of my groups. And as a GM, I would never take responsibility for treasure disputes among the players. It is too easy to be perceived as playing favorites.

Second, you and Vanessa (and any other characters still nursing a grudge or taking part in these disputes) need to air your grievances, apologize to each other (and mean it), bury the hatchet, move on, and speak of it no more.

It's not that I predict this sort of thing will poison your game.
It's that this is demonstrably poisoning your game right now.