Complex sentence: Indeed, Coffin's pieces contain many dark notes mixed with humor or imbued with a sing-songy, deceptively childlike voice that is reminiscent of Sylvia Plath.
Split into simpler sentences: Indeed, Coffin's pieces contain many dark notes. Pain is often mixed with humor or conveyed in a sing-songy, deceptively childlike voice that is reminiscent of Sylvia Plath.