Decoy allows you to reduce the amount of damage you take. When cast, a Decoy will appear where your mouse pointer was when the spell was cast. The Decoy looks exactly like you but it does not move. If it is hit a lot, it will sometimes appear to walk a little bit.
Most monsters will attack the Decoy instead of you if the Decoy is closer. Cast a Decoy in front of you then stand behind it. Use it as a Human or Magic shield. In most cases the monsters will attack the Decoy instead of you, especially when it's closer. Some monsters have different ideas as to what to attack but even if all of the monsters don't attack the Decoy, any monsters attacking the Decoy instead of you is helpful. Many Unique Monsters are not fooled by Decoys.
Decoy is great from level 24 to 30 before you have a Valkyrie. Use Decoy a lot to help deflect fire. Lead monsters until they are on one side of you then cast a Decoy and hide behind it. Decoy is still useful once you get a Valkyrie. The Valkyrie attracts the fire of some monsters but there are still situations where Decoy will help out. When there are a lot of dangerous ranged attackers hitting you, cast a Decoy. The Decoy will absorb some of the fire. Also use Decoy when there are a lot of monsters that you cannot quickly kill.
Hot key Decoy so you can easily cast it.
Decoy is a good monster detector. Cast a Decoy up ahead of you and see if it is hit. If so, you know there are monsters ahead. Walk up and stand behind the Decoy and use it as cover.
If you are hit while casting Decoy, your spell casting will be interrupted and the Decoy will not appear. If you are hit while casting Decoy, cast the Decoy again. With % Mana Steal items you can quickly recover your Mana.
The Decoy will only last as long as it has Life. Decoys have the same Life as the casting Amazon. Decoys will be destroyed if they take too much damage. The duration time for Decoy is only the case if the Decoy doesn't take enough damage to be killed during that time.
Strafe will fire more Arrows if you have a Decoy out which is another good reason to use Decoy.
Some players can be fooled by Decoys in player vs. player battles. Not everyone is aware of this skill.
The Decoy has resistances and skills like Evade and Dodge.
Decoy Resistance = level * 4, capped at 85.
Amazons derive another benefit while learning to fight in the rainforests of their homeland. They learn, through misdirection and deception, to fool attacking forces into thinking there is another Amazon nearby. This subterfuge causes enemies to waste time and energy hunting down false prey while the Amazon moves in for the kill.
↑Diablo II Manual, page 58. Blizzard Entertainment, 2000.