My favourite so far
What a wonderful puzzle this is. The mechanism is absolutely fascinating. It is a 4x4 masquerading as a 3x3x4, and the internals work similar to a 2x2, so you only need 2x2 algs to solve it. I don't want to spoil the solution here, but it is so much fun, and so challenging that it is now among my favorite puzzles. I highly recommend this.