The Twin TriTangle puzzle is essentially two TriTangle puzzles sharing a single core. There are twelve axes, only six of which are initially available. For the first couple of moves, the puzzle behaves like two separate TriTangles. However, the "stored" axes allow the pieces to interchange between the two TriTangles, provided those axes are not blocked by the large spikes. This makes the Twin TriTangle more challenging to solve than the original TriTangle puzzle.
The Twin TriTangle puzzle comes as a DIY kit of parts, and you will need to supply your own stickers. The templates for the stickers are available in the instructions forum.
I recommend that unless you are familiar with the process of dyeing these parts, you purchase the puzzle in "Black Strong & Flexible". It costs a bit more than the white material, but it's worth it since the finished puzzle will look and work better. Twin TriTangle also requires twelve black 12mm M3 screws to assemble, which you will need to purchase separately.