The Twilight Runes Spring Fairy was released as part of the 2014 Birthday Party event on May 5th, 2014. A Twilight Runes egg could randomly be brought back by exploring horses, but its species would not be revealed until hatching. This color cannot be passed down to offspring.
The Eternal Youth pose was released separately on August 30th, 2014, as part of the Back to School event. It is not currently obtainable through other methods.