@JeremyECrawford if I truepoly a player into another humanoid and it gains levels, then reverts to its original form (from whatever cause), how does that experience translate? Does it lose its new levels? #dnd
— Rolling With Disadvantage Podcast (@RWDPodcast) December 23, 2019
When your character gains XP in D&D, they can't lose those points.
Also, experience points belong to the person, not the form the person was in when they gained the points. #DnD https://t.co/UCcrma6OUE
— Jeremy Crawford (@JeremyECrawford) December 23, 2019
On the subject of XP I’m being told that official adventures are purposefully calling leveling without using XP “Milestone” instead of Story-based and that the entry for Milestone in the DMG is out of date and unofficial now. Is this so? Adventures can do all sorts of ad hoc things. Those exceptions don't invalidate the core rules.
As for your specific question, we have no planned errata for the section on milestones in the DMG.
— Jeremy Crawford (@JeremyECrawford) December 23, 2019
The Fool card in the Deck of Many Things does, indeed, take away XP. That's a great example of an exception in D&D. No general rule removes XP. But an exception in the game—whether in the rules or in the DM's rulings—isn't bound by the general rules. #DnD https://t.co/zVsamnYE0J
— Jeremy Crawford (@JeremyECrawford) December 23, 2019
The Fool card in the Deck of Many Things does, indeed, take away XP. That’s a great example of an exception in D&D. No general rule removes XP. But an exception in the game—whether in the rules or in the DM’s rulings—isn’t bound by the general rules. Every D&D rule has an invisible companion, ready to jump into action at another rule's command or at the command of the DM. That companion says this: "That rule says X, and X is true—until I say it isn't." #DnD
— Jeremy Crawford (@JeremyECrawford) December 23, 2019