Headscratchers / Avengers Undercover

• Daimon Hellstrom is usually an Anti-Hero of the "brooding, struggling to control his darker side, but ultimately good" variety. Suddenly he's not only a villain, but a henchman of Baron Zemo who chows down on popcorn alongside Constrictor and Madam Masque while watching the Academy kids getting beaten by Arcade. When did he become evil? What does he stand to gain by working with Zemo? And why has his personality changed so? Was this change ever explained or is it just blatant Character Derailment?
• Is there a reason for Zemo to keep Arcade alive? With the duplicate in his place Zemo can control all of Arcade's property while maintaining the pretense that he isn't a tyrant. Leaving Arcade alive only makes it possible for him to later cause problems for Zemo.