Complex sentence: Tin Tower is the tallest building in Ecruteak City, and was built to replace the Brass Tower after you obtain the Rainbow Wing, Ho-oh will be at the top of the tower, waiting for you to catch it.
Split into simpler sentences: Tin Tower is the tallest building in Ecruteak City, and was built to replace the Brass Tower. After you obtain the Rainbow Wing, Ho-oh will be at the top of the tower, waiting for you to catch it.