Complex sentence: The Joker temporarily escapes justice when Ayatollah Ruhollah Khomeini appoints him the Iranian ambassador to the United Nations, giving him diplomatic immunity; however, when he tries to poison the UN membership he is brought down by Batman and Superman.
Split into simpler sentences: The Joker temporarily escapes justice when Ayatollah Ruhollah Khomeini appoints him the Iranian ambassador to the United Nations, giving him diplomatic immunity. However, when he tries to poison the UN membership, he is brought down by Batman and Superman.