Complex sentence: As the Joker is about to escape in a helicopter, Batman ties a grappling hook onto the Joker's leg and attaches it to a stone gargoyle, but the Joker falls to his death when the gargoyle breaks loose of its moorings.
Split into simpler sentences: As the Joker is about to escape in a helicopter, Batman ties a grappling hook onto the Joker's leg and attaches it to a stone gargoyle. The Joker falls to his death when the gargoyle breaks loose of its moorings.