Rulings

• Being harnessed isn't copiable. If something else becomes a copy of The Soul Stone, it must be harnessed separately. Similarly, if The Soul Stone is already harnessed and becomes a copy of something else, it stays harnessed, though it's very likely that won't be relevant until that copy effect ends.2025-09-19
• "Harnessed" is a designation that the permanent has once an ability instructs you to harness it. It has no special rules meaning other than being a designation that the ∞ ability (and, theoretically, other effects) can see.2025-09-19
• Until it is harnessed, The Soul Stone doesn't have the ability listed after the infinity symbol. It also doesn't have that ability in zones other than the battlefield.2025-09-19