TIFU by disintegrating our DM's GF in DnD

Not today, but last night. This is a long story, but I'm not a monster and will include a TL;DR at the bottom- but in order to understand everything if you aren't into DnD, you may want to read the whole thing.

Our campaign started 6 months ago. Our party includes a wizard (me), a barbarian (DM's GF... lets call her "Barb"), a warlock, a paladin, and a ranger. If you aren't familiar with how DnD 5E works with it's class balancing, it's basically this: melee classes are gods levels 1-10, caster classes quickly overtake and surpass them at levels 11-20. Some of the late game stuff you can do with a sorcerer/wizard/warlock makes the early level slog so much worth it.

So this was our DM's GF's first DnD campaign, and she quickly fell in love with it. I have played many times and know the ins and outs, but it was enjoyable. For most of the early campaign, the warlock and I supported the paladin and Barb's goals: paladin wants to create an order of paladins for him to command, and Barb wants to become a barbarian queen. The warlock and I have much simpler goals: I want to become a god, and the warlock wants to become the #2 to his devil patron. The ranger owed a lot of money to a crime lord and is looking to pay it off.

So as the game goes on, the paladin and Barb carry me and the warlock through most of the early campaign. We deal with them making fun of us for being "weak magic casters" while they go off and melee with strong overlords and monsters. 5 months into the campaign, we finally reach level 16. At this point, the warlock and I have abilities that let us snap our fingers to change reality. Barb and the paladin are now being carried by us.

My character is a divination wizard with the lucky feat. If you aren't familiar with DnD 5E, divination is pretty simple: I make 2 dice rolls at the start of every day. These rolls are called "portents". I can then decide to substitute any roll with those portents, essentially letting me decide what someone rolls. Which is POWERFUL: I can decide who succeeds and who fails. The lucky feat also lets me reroll anything that affects my wizard. So if I roll a natural 1 (critical failire), I can use the lucky feat to reroll that outcome. Combined with portent, I can pretty much alter reality as I see fit- without using any wizard spells. My wizard also specializes in psionic-type magic- pretty much anything that deals force damage, enchantment, illusions, and teleporting.

This all comes to a head when we fight one of the big bad enemies we had been dealing with for most of the campaign. We defeat her, and the paladin and Barb want to show her clemency as she begs for her life. I use the detect thoughts spell, and the DM tells me she's lying through her teeth- the minute we leave, she's going to try and recoup everything she lost. I decide to blast her with the Feeblemind spell: It's basically a mindwipe, and if they fail their intellligence save, they can only make the save again after 30 days. Which means, potentially, if a person fails their save every month, they could be mindwiped for a very long time. And since feeblemind reduces their intelligence to a 1, their save also includes the negative modifier. It's a pretty nasty spell.

Well, I use portent to force her to fail her save, and the DM explains to Barb what I did, which deeply upset her. I didn't find out until after the session, but her grandma has dementia, and I basically used a dementia spell. Oops. After a month of wrapping up loose ends, we're level 18. The paladin has his order of paladins, I have a stash of clones and copied spell books in a demiplane as body backups, the warlock has cozied up to his patron, and the ranger has paid off his debt and is quite wealthy.

The only loose end we have, is Barb is looking to become a barbarian queen. Thankfully, there are many kingdoms in our world, and I'm a wizard. Feeling bad for slightly traumatizing her, I tell Barb, "pick a kingdom, and I'll give it to you." She's a little confused by me saying I'll give her a kingdom, but she chooses one and I get to work. Now, being a level 18 Wizard, I have access to the Wish spell- which is basically a backdoor to every spell up to level 8 in every class.

I use Wish to cast what is probably the most insidious spell in the game: Glibness. Glibness works like this: any charisma roll I make will at minimum be a 15. This basically means, whatever I say, people will believe me no matter what. Any spell they use to determine if I'm lying or not will be rendered moot, as Glibness overwrites that spell to make it look like I'm telling the truth. So after casting Glibness, I go into the capital city of the kingdom and begin telling everyone Barb is their new queen and ruler, and they love her. Because all my charisma checks are 15, they believe me. Glibness is a mass-brainwashing spell if you haven't figured it out. Before the hour is up, I have everyone in the capital, including the former king, believing Barb is their new queen, and they love her.

While this is happening, Barb- out of character- is horrified by what I'm doing. I return to Barb -in game- after a long rest, and let her know her new kingdom has crowned her queen and it's all hers. Barb exclaims what I'm doing is evil and challenges me to a fight to the death. I tell her, "I got clones, FYI, any time you kill me, I just upload to a new clone body. If you feel so strongly, we should probably just split ways". She doesn't care and wants to fight me anyway. So I toss my spell book into my demiplane and we roll for initiative.

A level 18 Barb has a shit ton of hitpoints and AC. There is no way I'm whittling her down before she kills me, so I have to resort to one of my one-hit-kill moves, which a level 18 wizard has in spades. I use one of my three portents to fudge her initiative roll, making me come out on top. My first spell is polymorph. She goes to make her wisdom save, but I use my 2nd portent to fudge that, and turn her into a crab.

I ask Barb out of character, if I show mercy to her barbarian, will she leave me in peace? Barb promptly tells me she'd hunt me to the ends of the earth, and use her new brainwashed kingdom and it's resources to do so. So I cast the Wish spell -> Plane Shift, and I sent the polymorphed Crab-Barb to the elemental plane of fire. Normally, this would be a death sentence, as the crab would be rendered to 0 HP, and change back into Barb, and then Barb would be trapped in a forever burning plane of torment that would quickly burn her to death.

The DM, not wanting his GF to die, said after doing this a portal opened from the plane of fire, as a fire efreet kicked her out. She was at 5 HP, and covered in severe burns. Barb is pretty upset, and I give her one last chance to back down. She doesn't and I use a disintegrate spell. I use my last portent to fudge her dex save, and Barb is no more- not even the DM can save her, and the paladin can't rez her without a body.

At this point, Barb rages at me IRL, and the session is done... and we're probably done with the campaign for the foreseeable future (divination joke)

TL;DR: my psychic wizard brainwashed a kingdom into making a barbarian it's queen, and this pissed off the barbarian, who decided to kill me. I banish her to a plane of everlasting torment, but the DM saved her out of pity. Barbarian wouldn't back down, so I thanos snapped her into dust. Our DnD group may not recover.

Everyone but the DM's GF doesn't think I'm the bad guy in this situation.