What if Rotom holds a Z-Crystal and changes form?

Question

Hi! I am just wondering. What if, for example, Heat Rotom holds a Firium Z then turns into Wash Rotom?

Answer 1

Nothing will happen. Rotom will change its form.

Comments

i mean change his form outside of battle while it is holding z crystal

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It will become a wash Rotom holding a firium Z.

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the same happens with necrozma fusing, or move the move deleter

Answer 2

Any Pokemon holding a Z-Crystal that loses the move it uses/changes to a form incompatible will still hold the Z-Crystal, it just cannot use it.
Source: Experience

Answer 3

Rotom will still have the Z-Crystal but will be unable to use it unless it knows a compatible move for said Z-Crystal. If your Rotom knows Sunny Day or Will-O-Wisp then it will be able to use the Firium Z.