A Plague Tale: Innocence puts a great emphasis on the elements of stealth. Because of that, Amicia has only her sling as a weapon, which has its limitations. The next section will tell you how to avoid detection, and how to act when it happens.
At a time when your attempt to divert the attention of the enemy fails or unwittingly draws the attention of the enemy, you will have to fight. Escape is not an option because Amicia is too slow to escape. You can try changing the cover. If you manage to do it without the enemies noticing, they will stop looking for you.
Slingshot allows you to eliminate an enemy without a helmet. If you can do that, the danger is averted. Just aim and shoot. If your target is wearing a helmet, then you can't do any damage to them until Chapter V. Only after meeting Lucas will you get a recipe for Somnum . This is a tranquilizing potion that will allow you to put the enemy to sleep. In this case, during an attack, it will be possible to use the potion. Always carry at least one to avoid an otherwise preventable death.
In Chapter VII, Melie will explain to you how to create the Devorantis . It's a substance that burns through metal. Hitting an enemy in the head with a bullet like that will make them take the helmet off. This will expose them to a shot with the sling, and you will be able to eliminate the enemies freely.
The last way to get rid of the enemy is the use of rats. If the rats are near an enemy, you can lure them to him. When he carries a lantern, you can put it out. This will make the rats attack. For this, you can also use Odoris. This potion lures rats to a specific point. If you throw it at the enemy, the rats will attack him. In this case, however, it is necessary to keep the victim outside an external light source.