Constitution Boon (Grim Alteration)
From D&D Wiki
With a gritting of his teeth, he stood straight and stoic.
Description: While Transformed, he gains a +2 enhancement bonus to Constitution.
Special: The temporary hit points granted by this ability pool for the entire day. They are not refreshed every time a grim Transforms, though he does regain them if they went unused from a previous Transformation that day (so long as he had any left to regain).