Complex sentence: D'Ken, who was a very corrupt leader, attempted to use a powerful crystal, known as the M'Krann Crystal to take over the universe, but the X-Men and D'Ken's younger sister, Lilandra killed him before he was able to carry out his plans.
Split into simpler sentences: D'Ken, who was a very corrupt leader, attempted to use a powerful crystal, known as the M'Krann Crystal, to take over the universe. But the X-Men and D'Ken's younger sister, Lilandra, killed him before he was able to carry out his plans.