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human
[Fullmetal Alchemist: Brotherhood] If Pride happened to absorb Greed like he said he could, what benefits could that grant him?

Considering Pride's shadows are an extension of his body, would Greed's ultimate shield benefit Pride's childlike form, or would Pride's shadows be able to transform into an indestructible carbon-based substance?
gpt
It's not clear that there would be any benefit to Pride, other than a small stroke to the ego.

 Pride, despite his small stature, is the de facto leader of Homonculus by virtue of his immense martial strength and power. This has to be somewhat embarrassing for Greed, who is very clear about not taking orders from anyone but himself, especially when the person giving out orders appears to be a child. When Pride threatens to absorb him, Greed backs off immediately because he knows that Pride could wipe him out in an instant. This shows a deference to Pride that the other homunculus seem to show as well. 

When a Homonculus "dies" their powers can be reallocated to another physical vessel (e.g. the first body that contained Greed gave way for Greed to inhabit Ling's). This has got to be embarassing for Greed, as greedy people generally do not like having things taken from them, especially super powers. Pride knows this, and knows that he could kill Greed in an instant, so absorbing Greed is less of an injury and more of an insult. 

Alternatively, we know that Greed's ultimate shield works by manipulating physical matter. It's not clear what Pride's shadows are, but they seem keen enough without needing the additional fortification of Greed's ultimate shield. A neat application would be deploying the shield between a light souce and Pride, creating the shadows necessary for him to use his powers.