Splinter Twin is one of many Rise of the Eldrazi cards being reprinted in Modern Masters 2015. As of the announcement, it's been a $25 card. Other expensive Rise cards like All is Dust, Kozilek, Butcher of Truth, and Ulamog the Infinite Gyre are being reprinted at their original mythic rare status. Twin is only a rare, so it's likely going to see a noticeable dip in value.
To be fair, however, Splinter Twin a four-of in any Twin combo deck. Even though the supply will grow sharply, and the price may plummet at first, it should be a good long term value as the Modern Masters 2015 copies are swept up.