Well first is first, you have to catch regirock. Visit the rock peak chamber at day and at night. After having visited it at both day and night, a puzzle should appear on the floor. To solve the puzzle, walk to the center piece. Then, without pressing any buttons, walk six down and then nine right. Then, press a. This should make regirock appear the next time you visit the chamber, if not immediately. Catch regirock, and you will obtain the iron key. With this key active, as opposed to the rock peak key, Registeel will appear in the same room where regirock was the next time you visit.
Yes that is very confusing. Ill try to sum it up.
Visit the rock peak chamber room at day and at night
A puzzle should appear. Don't press any buttons. Wall to center tile. From there, walk six steps down and nine to the right. Stop. Press a. A hidden switch will be activated.
If regirock does not appear, leave and reenter the chamber. If its still not there, you need to do the puzzle again. If it is interact with and catch him, and you will obtain the iron key.
Activate the iron key, which can be activated in the "mystery door" section of the Key Link.
Return to the same room where you caught regirock. Registeel should appear. Interact with it to battle it.
I know it is a long and confusing process but I hope this helped.
