DM Q&A: RP'ing other forms than are in game

[Lady Frost]

What are the general guidelines for roleplaying forms that your character cannot turn into in-game? Polymorph Self, Shapechange, Wildshape, etc

For example, is Shapechange limited to only those 5 forms? Is it limited to those basic types of forms? Dragons, Giants, Golems, Slaadi, Fiends

My personal example uses Lavina. She's an epic transmuter with Shapechange. I specifically ask because in RP, a fire giant and red dragon wouldn't suit her at all and she'd use the spell more likely as a frost or storm giant, and white or silver dragon. In-game, I understand the constraints, but in RP, I'd like to know what the expectations are for the creative use of these spells.

Thanks

[DM Hawk]

Generally, characters are limited to the mechanical forms as supported by spells / class feats in game.

Characters may potentially assume shapes beyond this temporarily in an event if they have agreement from the DM or EDM running the event. Additionally, a character may have access to expanded forms through a DM reward item.

There is an open project to expand options for wildshape feats and spells like Polymorph Self and Shapehange. If this rolls out successfully downstream the general guidance above would still apply.