Alexander I's elated, mystical, and even messianic mood expressed itself best in a remarkable and peculiar document known as the Holy Alliance.

Окрылил, мистическ и уже мессианск настроение в Александер I выражало себя лучший удивителейё/ой документ известноте Великая Союзу.

Masculine adjectives-endings removed

Великая - accusative adjective
Союзу - accusative since it is direct object

"mood" - is nominative?

I don't know what to do anymore.