Intimidation is all about perception, especially with a Pokemon's movepool and appearance.
Steel-type Pokemon are some of the most intimidating around. Most of them are massive and just look downright angry. They are known for being sturdy and powerful.
This list isn't going to have Bronzong, Alolan Sandshrew, or Klefki. While they are fine Pokemon in their own right, they are nowhere near as intimidating as some of the following creatures.
Note: This article is subjective and reflects the opinion of the writer.
Top 5 most intimidating Steel Pokemon of all time
#5 - Aggron
Aggron is a huge Pokemon. It has all the looks of an intimidating monster. Its body looks like an iron suit of armor. Its horns can cut through steel and it wears its battle scars with pride. There was even once a king who wore a helmet resembling the head of Aggron. He hoped to channel its strength and intimidate his enemies.
#4 - Lucario
Lucario is so cool, and it is hard to not feel intimidated when going up against this Fighting/Steel-type Pokemon. It is almost as if nothing bothers Lucario, especially in battle. It is there to fight and it does that very well. Every time Lucario has made an appearance, it has been iconic.
#3 - Metagross
The size of Metagross, along with its Psychic-typing, is enough to send any opponent running. The red eyes really hammer home the intimidating factor. As a psuedo-Legendary, it is one of the most powerful Pokemon to ever exist. It also has one of the lowest catch rates of any non-Legendary. Maybe that has to do with it being so terrifying?
#2 - Scizor
Scizor is intimidating in the same manner as Lucario. It just looks ready for a fight. Scyther was already a powerful Pokemon. Imagine the first person to discover its evolution and realize that it can get even more powerful. Its sleek red coloring and massive pincers are super intimidating. Scizor is enough to leave anybody shaking opposite of it.
#1 - Steelix
While Steelix may not be the most popular Steel-type Pokemon in battle, there is no argument against it being the most intimidating. This evolution of Onix is downright frightening. It is a massive iron snake. Its face is really scary. Any Pokemon standing across the battlefield from Steelix has plenty to worry about.