As a former 5th tier Raid Boss, Registeel's CP was 33,516. Its maximum capture CP in Bonus Challenge was 1,398 and 1,748 when encountered Pokémon was boosted by weather.
Registeel was available in Raid Battles from July 19th, 2018 until August 16th, 2018.
During March to April 2019, Registeel was the reward of the Research Breakthrough once seven stamps had been obtained with a 1,048 of maximal CP.
Registeel is considered by player community as a part of the "Regi" Pokémon family — Regirock, Regice, Registeel, and Regigigas (Sinnoh-region Pokémon), but none of them is related with each other by evolution.