Complex sentence: Dreadwing refuses to oblige to Megatron's order and raises his sword in an attempt to kill Starscream, but Megatron kills Dreadwing in self-defense as he tells Starscream not to make him regret on who he chose to spare.
Split into simpler sentences: Dreadwing refuses to oblige to Megatron's order and raises his sword in an attempt to kill Starscream, but Megatron kills Dreadwing in self-defense. Afterwards, Megatron tells Starscream not to make him regret on who he chose to spare.