Complex sentence: As Bucky and Black Widow are attacked by Ares and Venom, there are flashbacks to Steve Rogers, who appears on D-Day, his mother's death, and then back in D-Day with Bucky from that time.
Split into simpler sentences: As Bucky and Black Widow are attacked by Ares and Venom. There are flashbacks to Steve Rogers, who appears on D-Day, his mother's death, and then back in D-Day with Bucky from that time.