Registeel Shrine
The Registeel Shrine is used to spawn the legendary pokemon Registeel
To spawn Registeel you need 3 Things
1. The Iron Key
2. A Regigigas In your party
3. 9 Unown blocks spelling out R-E-G-I-S-T-E-E-L
Learn how to craft certain Unown blocks Here
You then need to find a Regice Shrine. These spawn in mountainous, hills biomes or mesas
Once you have all items required; and you have found the shrine you need to place all 6 Unown Blocks onto the Temple Pillar blocks, (in the right order, spelling out Registeel with them.
Then you need to right click the shrine with the key in hand.