I'll try to go with Stone Form
Yes it should work for you too.
I have just tried to make Stone Form work in Reforged, but with a lot of tinkering around, i always ended up with one issue or another.
This said, I nearly completely managed to get it to work with a single custom version of the Storm Crow Form unit ability.
For some reasons, making a different version to switch back created issues.
So what I did basically is use the same tag, attachment and bone names as the Crow Form of the Druid of the Talon and replaced them with the animation tag my model uses for the desired "look". This tag is "victory".
Then I removed requirements, mana cost, zeroed all duration fields.
With just this, only the portrait was showing the proper animation, and as trying to change the model animation tag in my previous tests had the opposite problem, i just play the "stand victory" animation and it seems to work.
As the vertex coloring and the Proper Name of the Flying Ball that needed to change did not follow the model change, i fixed that with a couple of actions.
As I can only use a single ability for both transformations, i just check the Unit ID and it seems to do the job.
I made a GUI version of the trigger I used just to show for anyone interested to get this to work in Reforged but who would not be familiar with Lua :
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ChangeModelWithPortrait
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Events
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Unit - A unit Finishes casting an ability
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Conditions
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(Ability being cast) Equal to Roast
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Actions
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If (All Conditions are True) then do (Then Actions) else do (Else Actions)
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If - Conditions
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(Unit-type of (Casting unit)) Equal to Flying Ball Test
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Then - Actions
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Animation - Add the victory animation tag to (Casting unit)
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Animation - Play (Casting unit)'s stand victory animation
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Animation - Change (Casting unit)'s vertex coloring to (100.00%, 100.00%, 100.00%) with 0.00% transparency
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Hero - Set Name of (Casting unit) to Roasting Flying Ball
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Else - Actions
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Animation - Remove the victory animation tag to (Casting unit)
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Animation - Play (Casting unit)'s stand animation
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Animation - Change (Casting unit)'s vertex coloring to (47.00%, 78.00%, 100.00%) with 0.00% transparency
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Hero - Set Name of (Casting unit) to Flying Ball
The only small issue I have is that the stand animation does not seem to work properly when the Roasting Flying Ball changes back to Flying Ball.
But it does not matter much as the model starts to change back properly again as soon as the Flying Ball starts moving (strange as the walk animation should have no effect on the tag).
@Daffa +rep to you for leading me to tinker with this (when the 24h will expire lol)
I didn't manage to get a countdown progress bar working with Stone Form or Storm Crow Form, but I guess I can still use the one I made out of UI Frames.
Note that if you have any idea about getting the progress bar to work, let me know : I tried adding a generic expiration timer but the progress did not show, only the generic progress bar looking frozen (the unit indeed expired though).
I quite like my custom UI progress bar, but it is quite complex, so anything that I could replace with features integrated in the game engine would be really welcome.