Johto was the region where Steel-type Pokemon were introduced into the series.
Generation II literally changed the game. New types were added. Trainers were taken to a brand new region. It also packed two regions into one game with Gold and Silver.
Steel-type were implemented to give more defensive options for battling. They are sturdy, powerful juggernauts. These Pokemon are very hard to take down, even with supereffective attacks.
Top 3 Steel Pokemon from Johto
#3 - Skarmory
Skarmory introduced an incredible type combination with Flying/Steel. It is only weak to Fire and Electric. It has immunity to Ground and Poison. Six types do normal damage and the rest, it resists. That is an insane amount of resistances.
With a massive 140 base Defense stat, Skarmory is a wonderful staller. Flying moves and Steel-type moves give this Pokemon amazing coverage. Overall, Skarmory is one the best Flying-types, and that's not just in Johto.
#2 - Steelix
There were plenty of trainers fearful of Onix. This giant rock snake was the first true test for trainers in the Kanto region, as Brock's one dominated the Pewter City Gym. As Johto was revealed, so was the Iron Snake Pokemon, and Onix's evolution, Steelix.
Steelix is way more terrifying in appearance than Onix. It is also way more defensive. That is saying a lot, because Onix has a huge Defense stat. Steelix's comes with a 200 base Defense. Steelix is a powerhouse of a creature.
#1 - Scizor
Scyther was one of the most intimidating Pokemon in Generation I. Most Bug-types are considered weak, but not Scyther. In Generation II, that power was increased with an evolution that no one expected. Enter Scizor.
Scizor is just plain cool. The sleek red and a singular weakness to Fire makes Scizor a force to be reckoned with. It isn't the fastest Pokemon, but it has great Defense at 100 and insane Attack at 130.