An Aura instance refers to the individual applications of a specific aura, how many times it was applied, and more importantly when it was applied. Within these aura interactions are the interactions between the various modifier and derived stats themselves, but beyond this auras can be generally categorized as either being similar, or non-similar. Similar auras are auras who share the exact same name, and non-similar are those with different names, therefore, two auras having the same effect is not the same as two auras being identical. Below you will see a brief description of the interactions between these two categories as well as a few examples of said interactions.
Similar Auras are auras that share the same name, these auras interact in two ways:
Non-similar auras are simply auras with different names, regardless of the effect tied to the aura, they interact in the usual manner:
In this section we will be looking closely at how similar-stackable auras interact with one another since these are the only real oddity concerning aura interactions. We will also be looking at how similar DoTs interact with one another. For reference, we will be using terms such as Highest or lowest instance quite a bit, this in simple terms just refers to the latest applied aura and the earliest applied aura respectively.
DoT Trading refers to the interaction between similar DoTs, where the DoT is 'stolen' from the highest instance by the lowest instance. In the video above you will notice that upon applying 'Shadow Smoke' a DoT is initiated. Danzon applies the first instance and gets 2 out of the usual 4 ticks that you would apply under this aura. After 2 ticks Nix applies his own 'Shadow Smoke', and takes away Danzon's DoTs for himself, despite 'Shadow Smoke' never fading for Danzon, he no longer has an outsource of DoT damage. This cyclic back and forth of taking another's DoT is what constitutes as DoT Trading., the most recent instance takes away the earliest instance, yet the effect stays up for both participants.
This is one of the few ways that a non-loopable effect tied DoT can be looped, however, each DoT trade acts out as if the aura faded, in terms of stackable DoTs, therefore, each trade will revert back to the base value of the individual DoT and DoTs can not be stacked using this method.
As previosuly stated, Similar-Stackable auras compound with one another, and since these stack will be of the same modifiers, then it follows that that they would always interact additively with one another. In the example above we have two Frostval Barbarians using 'Silver Maw/Thaw/Jaw'. This skill applies 3 stackable effects, one reduces mana cost by 15% with every stack, one increases crit chance by 10% with every stack, and the other increases crit damage by 20% with every stack. In this example we'll be looking closely at the mana cost reduction buff. At full stacks of silver thaw, you and your party will be experiencing a mana cost reduction of 60% at full stacks, with two Frostval Barbarians in play this maximum is doubled, to a mana cost reduction of 120%, which means that your skills would cost -20% extra mana, or in other words, gaining 20% extra mana.
Silver Thaw is a skill which 'heals' 20 mana for the user, which means that it will have a mana cost of -20. From the 16s mark onwards you will notice that 'Silver Maw/Thaw/Jaw' is actually costing mana, rather than gaining it. This is because we've essentially turned a negative mana cost into a positive mana cost when introducing a mana cost reduction >100%. The skill now consumes 4 mana per use, which is a result of the following calculation: -0.2*-20 = +4.