How exactly Poe was transformed into a raven was never explained in the series. Although Magica has various transformation spells at her disposal, she is unable to turn Poe back into an anthropomorphic duck. In the episode "Send in the Clones" (1987), Magica explains that she needs the power of Scrooge McDuck's Number One Dime to restore Poe to his normal self, indicating that she means to turn him back. On top of that, Poe only appeared in some of the episodes featuring Magica and rarely did anything to advance the plot. Poe's most notable role was in the episode "Magica's Shadow War" (1987), in which a trapped Magica sent him out to find help in one scene.
Poe appeared rarely in DuckTales comics, including "The Ex-pilot" (1990) and a cameo in "Rightful Owners" (2011).
Darkwing Duck comics
Poe appeared in the Darkwing Duck story "Crisis on Infinite Darkwings (2010)", where he is looking for Magica and Negaduck after getting lost in the universe of two-headed people. He also made a cameo appearance in "Dangerous Currency" (2011), where he gets some slime on him--this is how Magica discovers how the slime works.