Is it possible to create a first-person shooter in Adventure Game Studio?
Yes, you just hide your main/player character.
Look, many of your recent questions could be answered by reading the beginners FAQ, or just browsing through the manual, and is what is insisted upon, before just asking questions in the forum.
http://americangirlscouts.org/agswiki/index.php/Graphics%2C_Characters%2C_Text_%26_Rooms#First-person_perspective_games_.28a_la_Nancy_Drew.2C_Myst.2C_etc..29