Complex sentence: Even his awesome new abilities proved no match for the Decepticon leader, himself recreated through Unicron's power, who used the Chaos-Bringer's power to wipe Starscream's mind, turning him into his right-hand man and most loyal subordinate.
Split into simpler sentences: Even his awesome new abilities proved no match for the Decepticon leader, himself recreated through Unicron's power. Megatron used the Chaos-Bringer's power to wipe Starscream's mind, turning him into his right-hand man and most loyal subordinate.