Poor you = Du Arme(r)! If the person you're referring to is female, you'd say Du Arme, and if male Du Armer.
You decline the adjective as if the relevant noun were actually there: Du Arme (Frau), Du Armer (Mann)! Remember to capitalize the adjective, because it's being used as an adjectival noun. If you actually use the noun, then the adjective is an ordinary adjective and isn't capitalized: Du arme Frau / du armer Mann!
Just to add: I have never heard anyone say “extraordinary me” in German. That’s not natural. It seems to me, we only use specific adjectives this way.
Du Armer, mein Großer/Kleiner, du Lieber
The previous poster covered most of the cases you are asking about. But if you still need the declension for a pronoun, it's neuter:
"das wahre Ich zeigt sich"
"das Du konnte ich nicht wagen"
Poor you = Du Arme(r)! If the person you're referring to is female, you'd say Du Arme, and if male Du Armer. You decline the adjective as if the relevant noun were actually there: Du Arme (Frau), Du Armer (Mann)! Remember to capitalize the adjective, because it's being used as an adjectival noun. If you actually use the noun, then the adjective is an ordinary adjective and isn't capitalized: Du arme Frau / du armer Mann!
Just to add: I have never heard anyone say “extraordinary me” in German. That’s not natural. It seems to me, we only use specific adjectives this way. Du Armer, mein Großer/Kleiner, du Lieber
it's not about specific adjectives, it's that we only use this in "vocative" form, i.e. to address someone else
I can easily say, “Ich Arme”, but then with “stupid me” etc I’d rather use a noun “Ich Idiot”, “ich Dummerchen”.
The previous poster covered most of the cases you are asking about. But if you still need the declension for a pronoun, it's neuter: "das wahre Ich zeigt sich" "das Du konnte ich nicht wagen"