The Evil Twin 3x3x2 is a puzzle that appears to be a 3x3x2 Rubik's Cube, but is actually made by fusing two 2x2 puzzles at a 1x1x2 block to create a siamese 2x2, and then adding extra cubies to fill in the gaps. It adds to the series of evil twin puzzles that includes the 2x2, 3x3, and 4x4 evil twins. I designed these extensions to make the final product look like a 57mm 3x3x2, using 24 mm 2x2s. You can scale the parts if you want to use different sized 2x2s.. The build process is very simple and easy, and the puzzle is very fun to solve. I highly recommend that you make it for yourself, if you are able to.
I made and reviewed this puzzle for my video series Print It Yourself:
Below is a brief description of how to make this puzzle. If you want to actually see the process, watch the video linked above.
-Cut off an edge of each 2x2, so that they fit into the two "connector" pieces. Glue them into the connectors and you should have a siamese 2x2.
-Cover all of the remaining exposed corners with the 12 "extension" pieces. Then you will have a siamese 2x2 with 19mm cubies.
-Glue the 4 "cubie" pieces to fill the unfilled corners and finish the 3x3x2 shape. The way in which you glue them is really up to you; there aren't any combinations that will leave you with a heavily bandaged puzzle. Just be careful to glue each cubie to only ONE of the 2x2s in the siamese 2x2. I glued mine with rotational symmetry; if you want to see how mine was done, it's visible in the video linked above.
If you have any questions, I recommend posting a comment on my YouTube video as that is where you will get the fastest response. I don't check Thingiverse very often, so if you ask a question here, it might take a while for you to get a response.