Now to first mention, this is NOT my combiner contest entry. This could've been, but I didn't like the looks enough and I had another idea, which is now my contest entry. This one can be an example for the contest category.
Now, the two combiners are this somekind of magma creature similar to anlags I've built...
...and this wing-blader. Neither don't have names.
For the transformations to combine, the magma creatures legs hold flip-out feet and the parts they held in place move little outwards. The flip-out feet are fun, but they reduce flexibility of the legs, making them required to be mainly knee-straight.
Magma creatures torso turns around and the arms switch sides by elbow. The head ducks to the side. In the pic all that is finished.
Magma creatures transformed form, from the other side.
The wing-bladers body gets couple twists, the legs go back and arms too. A matoran connector piece is revealed under the belly. Finished forming in the pic.
Finished form on the other side. The feet of wing-blader lock to the blue pegs.
The 2 combiners join by their hips with the matoran connector piece.
Wing-bladers upper body now comes over the hordika body piece.