Unique Attack Modifier

Unique Attack Modifiers (formerly known as Orb Effects) are special attack modifiers that alter a Hero's basic attack to provide an additional effect. An example of this is Morbid Mask, which grants the lifesteal effect. Certain Hero abilities are Unique Attack Modifiers, such as Anti Mage's Mana Break. Not all attack modifiers count as Unique Attack Modifiers, such as Huskar's Burning Spear or the purchasable Diffusal Blade. This means that Heroes can combine a unique attack modifier with other non-unique attack modifiers like Burning Spear or Searing Arrows, making use of both at the same time

Priority
Multiple modifiers do not stack; for each attack one modifier always takes priority. The order of priority is as follows:


 * 1) Conditional Modifiers - Modifiers that only occur on some attacks and are not controlled by the player, such as Maelstrom (chance-based) and Mjollnir (chance-based). If a Conditional Modifier fails to proc then a Standard or Ability Modifier will be present on the attack (if applicable)
 * 2) Ability Modifiers - Modifiers granted by Hero abilities* (in Ability Draft the first UAM ability obtained will override later ones)
 * 3) Standard Modifiers - Modifiers granted by items (an item will take priority depending on which is the oldest in your inventory, or in the case of illusions the first slot in reading order)

* ''UAMs from hero abilities, such as Viper's Poison Attack, will only be overridden by conditional modifiers if they are set to Autocast. If they are Manually cast, they cannot be overridden.''

When attacking units (such as Spell Immune heroes or buildings) that are immune to certain Unique Attack Modifiers, other UAMs that can proc will be used, even if they are not prioritized. An example of this is having an Eye of Skadi and a Desolator, if the Skadi has higher priority. Because buildings are not affected by the Skadi, the Desolator's effects will be used instead.

There are few known exceptions: Eye of Skadi or Orb of Venom, and Lifesteal can be active at the same time. (Lifesteal is granted by Morbid Mask, Helm of the Dominator, Mask of Madness, or Satanic.)

Sources of Unique Attack Modifier
Abilities


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Items


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Orb-walking
Heroes with a castable Unique Attack Modifier are often known for being able to chase a fleeing enemy hero more effectively due to a mechanic known as orb-walking.

Hero attacks have a part of the animation called the backswing, which delays your next action, but can be cancelled without preventing the attack from inflicting damage to allow for a faster recovery from the attack animation. However, if you cancel a standard attack too early, no damage will be dealt.

The advantage of a Unique Attack Modifier is that since it is considered a cast animation, it cannot be cancelled by issuing another command during the important part of the animation. If a command is issued during the animation, prior to the attack point, the backswing animation will be negated entirely, allowing the hero to continue chasing their target as efficiently as possible. Without a Unique Attack Modifier this is theoretically possible, but extremely difficult, since you would have to issue the move command at the precise moment that the attack point is reached.

Harassing
Typically when you right-click on an enemy hero, the nearby (500 radius) creeps will aggro you, and attack you. When you cast spells on enemy heroes this is not the case. Using this to harass is often incorrectly referred to as "orb-walking".

Harassing with orb effects involves using abilities that have Unique Attack Modifiers. Select the ability once and click on an enemy hero, this is now considered casting an ability; nearby enemy creeps will not attack you. You can repeat this as many times as wanted. Right clicking the ground to move in between casts of your Unique Attack Modifier is where the 'walk' comes in, and allows you to land more attacks on a fleeing enemy.

Conversely, if you enable auto-cast for the Unique Attack Modifier and right-click on a hero, creeps will attack you.