
Varalash |

The glaive thing isn't the dm's rule, it's right in the ability.
"For example, a Medium transformative longsword can take the shape of any other Medium one-handed melee weapon, such as a scimitar, flail, or trident, but not a Medium light or two-handed melee weapon (such as a Medium short sword or a Medium greatsword). " So a 2h glaive can't change to a 1h rapier.
I plan on getting it added to a weapon we found, since 10k for transformative is cheaper than getting an entirely new +3 weapon.
Should note too that you can cross size classes - for example, transformative greatsword can become a large sized one-handed weapon.