Complex sentence: Midna's first appearance was in a trailer for "Twilight Princess" shown at the 2005 Electronic Entertainment Expo (E3); at the time, her gender was unknown, leaving some journalists confused about it.
Split into simpler sentences: Midna's first appearance was in a trailer for "Twilight Princess" at the E3 2005. At the time, her gender was unknown, leaving some journalists confused about it.