Complex sentence: Ego's pet empath Mantis grows close to Drax and warns him, Gamora, and Nebula of Ego's plan just as Rocket, Yondu, Groot, and Kraglin arrive.
Split into simpler sentences: Ego's pet empath Mantis grows close to Drax and warns him. Gamora and Nebula also learn of Ego's plan just as Rocket, Yondu, Groot and Kraglin arrive.