There are two main variants of the Armaduras: those in all-silver, and those with gold trimming. When walking by the ones that stand still, the player enters a quick time event where they must dodge their attack. Failure to dodge results and heavy damage. Whether the player dodges or not, the Armadura will fall apart and not come back.
The ones that move and attack, move as fast as the player but take frequent pauses letting the player keep distance so long they keep moving. Being shot at doesn't always cause them to flinch. Sustaining a lot of damage will cause them to kneel over. Taking so much damage to their weak spot will cause a plaga to burst out from the helmet. The silver ones will have type-A plaga while the black ones will have type-B plaga.
Two that stay still and attack are in the hall way. Six guard the King's Grail. Three normal silver ones and three stronger black ones. The ones you have to fight do not appear in Easy mode as the King's Grail is already placed in the King's statue's hands.
When playing as Ashley, because you can not attack them, you can only run. When taking the Serpent Ornament, it is important to start running immediately for the exit. Otherwise, the Armaduras will crowd the doorway making it very difficult to leave.
As Leon, a good way to kill an Armaduras is to aim a shotgun blast at their head. That will usually either stun them so that they need to recover their strength, or instantly reveal the plaga. Instead of taking all of them out one by one, you can expose all of their plagas and then throw a flash grenade, easily killing a boss in six to twelve shots. Be careful doing this, though - when you fight the black ones, they will spawn type-B plagas.
Another good way is to focus at one at a time; blow off their helmets with a shotgun and spray them with the TMP, quickly taking them out. This would be useful for the black Armaduras.