There have been several distinct lines of Transformer reissues over the years. The Encore line is a Japan-specific line that started in 2007. The molds used in the Encore line, themselves, are from the early part of the Generation One era (I don't think any mold released in the Encore line has origins more recent than 1987), but the toys themselves have varied between straight-out reissues of old toys and all-new characters, depending on how color schemes have been applied to the molds.
Twincast was a character featured in the 1987 Headmasters toyline in Japan. The Headmasters toyline, along with its associated cartoon, represents the point at which the American and Japanese versions of the Transformers franchise started to depart significantly from one another (the two would come back together, and drift apart again, many times over the years to come). While the American toys that came out in 1987 were featured on a three-part cartoon that ended out the American cartoon entirely, the Japanese toys of this year were given an entire 35-episode season, with even more seasons to follow for subsequent toys. In the Japanese Headmasters cartoon, Blaster was "killed off" in a battle with Decepticon rival Soundwave, only for both characters to be revived in the very next episode in new color schemes (thus, to sell new toys based off of those molds).
Both Blaster's and Soundwave's molds were changed a bit, allowing each to hold two cassettes, rather than just one, so as to give the toys some added playability beyond the new color scheme. In the case of the new version of Blaster, this explains the new name he was given: Twincast. This mold change is noticeable if you know what to look for, as the cassette door is considerably larger than it used to be, but it's nowhere near as glaring on Twincast as it is on the updated Soundwave (or later toys that used this same mold variation).
This 2012 reissue of Twincast is not a straight reissue of the original 1987 Twincast toy. The colors have been tweaked slightly (especially on the face, to more closely resemble the character's appearance on the cartoon), and all of the stickers have been replaced with tampograph applications. The cassette door (which originally had some molded detail added to further distinguish Twincast from Blaster) has also been smoothed out. Here is a side-by-side comparison (not taken by me).
It has become common (although by no means universal) for toys of these cassette-player characters to come packaged alongside cassette companions, and this version of Twincast is no exception. However, these toys are not reissues of previously existing toys. Although they do use molds that date back to the 1980s, these color schemes are completely new. Here are Nightstalker and Stripes, characters receiving their first toys ever, in cassette mode.
Although these are Nightstalker and Stripes' first toys, neither can properly be said to be entirely new characters. Nightstalker came from a UK text-only story published in 1986, and Stripes apparently originates from an early draft to the animated movie that came out that same year. In a nice twist, the toy designers decided to swap the weapons around a bit, giving Nightstalker the weapons usually associated with the Ravage mold (of which Stripes is a repaint), and giving Stripes the weapons usually given to Steeljaw (of which Nightstalker is a repaint). This further helps distinguish them from the original versions of these molds. I wish the toy designers would do this kind of thing more often!