Can True Polymorph be dispelled or reversed?

Question

My interpretation of True Polymorph is that, once made permanent, it could not be undone (except perhaps with a Wish spell, god-level magic, another casting of True Polymorph, or some similar ability). Spells like Dispel Magic would not affect a permanent True Polymorph.

However, in the comments of this question, dispelling True Polymorph is mentioned/briefly discussed. So, can any item or spell dispel True Polymorph once the transformation is permanent?

The linked question concerns whether the spell will naturally end, or if altering the polymorphed form (such as cutting the chunk of adamantine) will end the spell. The answers do not discuss the concept of dispelling the polymorph. My question is all about dispelling a permanent True Polymorph, and arguments about the spell ending through damage or other non-dispelling effects should not be considered here.

Answer 1

True Polymorph has received errata to clarify this. On page 185 of the SRD, the spell description now says:

The transformation lasts for the duration, or until the target drops to 0 hit points or dies. If you concentrate on this spell for the full duration, the transformation lasts until it is dispelled.

No more mention of “permanent” to confuse things.

As a result, concentrating on True Polymorph for an hour removes the need to concentrate, but nothing else — it can still be dispelled.

Answer 2

Crawford's November 2015 tweet addresses this.

http://www.sageadvice.eu/2015/11/01/can-permanent-magical-effects-be-dispelled/

A permanent magical effect can be dispelled unless the spell explicitly clarifies that it cannot be. True Polymorph fits into this category, which means that it can be dispelled.

This seems to imply that it's an ongoing magical effect even after the concentration ends, so presumably effects like Antimagic Sphere would also nullify the transformation.

Answer 3

Yes, True Polymorph can be dispelled. The spell description states for duration:

Concentration, up to 1 hour

Furthermore, the spells description states that:

If you concentrate on the spell for [1 hour], the transformation becomes permanent.

Note that an update in the SRD5 changed the wording of the latter to:

If you concentrate on this spell for the full duration, the transformation lasts until it is dispelled.

This cleared up the confusion regarding the "permanency" of the spell. Permanent, in this case, refers to the caster no longer requiring concentration. As such, effects that would break concentration do not interfere with the spell. However, a dispel can still end the spell as usual, reverting the target to its original form.

Answer 4

Yes or No (DM's choice)

As stated before by Eric, RAW for Dispel Magic says "Choose one creature, object, or magical effect within range... On a successful check, the spell ends."

So the DM has to arbitrate if the permanent status of True Polymorph is due to-

A) A self-sustaining magical effect that continually supports the new form. This supports this with the "...until 0 HP or dies" clause). In which case: Dispel, Detect Magic, Anti-magic Field, etc. will also have an effect on Polymorph.

B) The shift being akin to an instantaneous spell, which has already gone through it's magical effect. This is equally valid since it is a transmutation of living, non-magical matter to a different non-magical matter result. In which case, only altering reality or recasting polymorph (note the changing CR/levels and loss of gear) may work. Reverting back wouldn't be an option due to dispel, HP, death or non-epic magic.