Complex sentence: Once it evolves into Alakazam, it has mastered every type and form of psychic ability, and its brain continually grows, causing its head to become too heavy for its neck and requiring psychokinesis to hold it upright.
Split into simpler sentences: Once it evolves into Alakazam, it has mastered every type and form of psychic ability, and its brain continually grows. This causes its head to become too heavy for its neck, requiring psychokinesis to hold it upright.