Volo’s Guide to Monsters contains a Transmuter statblock, a humanoid of CR 5 with the following trait :
Transmuter’s Stone. The transmuter carries a magic stone it crafted that grants its bearer one of the following effects : Darkvision out of a range of 60 feet, An extra 10 feet of speed while the bearer is unencumbered, Proficiency with Constitution saving throws, Resistance to acid, cold, fire, lightning or thunder damage (transmuter’s choice whenever the transmuter chooses this benefit). If the transmuter has the stone and casts a transmutation spell of 1st level or higher, it can change the effect of the stone.
It is, I believe, possible for a high level caster to “morph” into a Transmuter statblock, either by True Polymorping into it directly, True Polymorphing into a creature that can then Change Shape into it (such as an Ancient Metallic Dragon), or Shapechanging into it.
My question is : if you “morph” into a Transmuter statblock, do you gain access to its Transmuter’s Stone ?