I know all of the seasons of the original Sailor Moon series had a variety of animators for each episode, but the artistic style and effects used in all of the various character transformation sequences are very similar. Who animated these?
Different episodes of the anime were directed by different Animation Directors, even within one season. The animators themselves and the artists who paint the backgrounds would have been under orders from the Animation Director and the Storyboard Artists rather than having personal freedom to decide the style and effects. It may be that the Animation Director of the episode in which a transformation sequence was introduced was allowed to propose, give input on, or approve the Storyboard Artists' proposition of how it would look. Finally, even amongst the Key Frame Animators drawing the actual cels, it is not clear whether or not one person would have drawn all key frames for the whole sequence. It is the responsibility of the Animation Director, Storyboard Artists, and Key Frame Animators to ensure that the character design and flow looks uniform despite the number of people drawing/painting various pieces of the final product.
Some of the sequences draw loosely upon the original manga illustrations by Takeuchi Naoko.