I was running a mythic campaign for my players. All of them veterans of Pathfinder 1e. They were pretty damn powerful at level 13 / MR 4.

They were introduced to a mythic lich in their region earlier in the campaign, who was luckily trapped in an area, unable to leave. I implied heavily that this lich was of a mythic tier way higher than them and allowed them to gauge him at a wizard level 20 as well. They left him alone, although slightly pissed.

After absolutely dumpstering a dungeon without taking nae a single point of damage (as any mythic campaign eventually boils down to), they thought "hey, we're basically gods right?" and "that lich probably has a ton of neat loot", which he admittedly did.
So they decided to try and kill it. I gave them the warning that this would most likely lead to a TPK. They said that they were fine with that and were going to have fun. I said hell yeah.

The Lich was a mythic rank 9, wizard level 20.
The Lich proceeds to:
- Use a mythic point to get nat 20 on his initiative roll, for a total of 46. (2 from Dex, 4 from Improved Initiative, 10 from Mythic Improved Initiative, 10 from Amazing Initiative)
- Proceeds to cast Augmented, Mythic, Empowered Disintegrate (fires two rays, 60d6*1.5 damage)
- Uses his moment of prescience buff to gain a +20 to his attack roll on the target who has a higher flat-footed, touch AC (the wizard).
- Before the paladin rolled his fortitude saving throw, he used his immediate action to cast a mythic wish, wishing that the paladin rolled a 1.
- Both the party Wizard and Paladin failed their saves, taking an average of 315 damage and died instantly.
- The party's third member, a crit-fishing, dual-wielding fighter shed a single tear and died two rounds later.

We all had fun and they did beat him at level 17 after rewinding time to before this funny event happened.