Edit. I made some mistakes at first. I retested it with mods.
This topic tries to describe the difference between AoE projectile skills and stackable AoE skills. Like Gnomish said, here is “same target affected” limitation in GD, ex. some skills don’t hit the same target twice in single cast/round.
Here are five dummies, and penetrating projectiles can pass through all 5 dummies.
Unstackable Penetrating Projectile
Evil Eye is an AoE Projectile skill, and Deception of Dreeg Set gives it 50% chance penetration. When player stand in a row with the dummies at Fort Ikon and attack the dummies.
Evil Eye + Vile Eruption (no Blood Burst)
Without Blood Burst, Evil Eye has a very small explosion range. When you’re lucky, the Evil Eye can pass through 5 dummies, and trigger Vile Eruption 5 times.
Evil Eye + Blood Burst (lv.12) + Vile Eruption
Evil Eye has a moderate explosion range. Evil Eye can pass through 5 dummies too, but trigger Vile Eruption only 3 times, exploding at Dummy 1, Dummy 3 and Dummy 4. And, every dummy only takes one direct hit*, even Dummy 2 is within the explosion ranges of Dummy 1 and Dummy 3.
(*direct hit means hit by Evil Eye itself, not by Vile Eruption.)
Evil Eye + Blood Burst (lv.22) + Vile Eruption
Evil Eye has a large explosion range. Evil Eye can still pass through 5 dummies, but explosion and Vile Eruption become even less, only bursting at Dummy 1 and Dummy 4. And, every dummy only takes one direct hit*.
(*direct hit means hit by Evil Eye itself, not by Vile Eruption.)
For projectile skills, all enemies it passes through will take only one hit, whether the explosion range is large or small, whether the enemy is dense or dispersed. Each enemy always takes only one direct hit regardless of enemy density and skill level of Blood Burst.
An interesting thing is that, high level Blood Burst will reduce Vile Eruption.
PRM is similar. Without radius modifiers, its base radius is very small (0.5 meter), and it almost explodes at every emeny to generate many fragments. Ludrigan Set and Vit PRM Conduit expend its radius, and then reduce explosions and fragments.
Aegis, not penetrating projectile, but bounce projectile, is similar. It won’t bounce to targets which have been hit by explosions in the same round, and every emeny will take only one explosion damage in a single round.
Stackable AoE
Ranged Primal Strike is a Stackable AoE skill, and Ugdenbog Sparkthrower gives it penetration ability. Similar, test it at Fort Ikon.
No matter how large the explosion range is, Primal Stike will explode at every dummy, and every dummy will suffer multiple direct hits. For example, Dummy 2 is within the explosion ranges of Dummy 1 and Dummy 3, then, Dummy 2 will takes 3 hits.
For stackable AoE skills, the larger the explosion range/the denser the enemies, the higher the damage each enemy takes. They can deal tons of damage to dense enemies.
Stackable AoE skills are rare. Common examples include ranged Primal Strike, ranged ABB, Explosive Strike and Upheaval. For melee Primal Strike and melee ABB, if there are modifiers adding their max targets, they are also stackable. I have tested it by mod.
Explosive Strike has another special mechanism. Normally, a second explosion will not be triggered before the end of one explosion. Like Torrent, there is always only one lightning chain at the same time. A second chain will not be triggered before the end of one chain.
If a single bullet pass through 5 enemies, 5 Explosive Strike can be often observed. But if several consecutive bullets (like chilling rounds) hit enemies in a very short period of time, explosions will be fewer, not all hits can trigger explosions. (I’m not 100% sure about this point.)
Melee Explosive Strike is even different. It seems that each weapon can explose respectively. Barthollem’s Warmaul Fire Strike (+4 target) causes only one Explosive Strike, but dual-wield Fire Strike causes 2 explosions, even two weapons hit at the same time (Shears and Whirling).
And finally, Focused Gaze will change Evil Eye to Grenade-like projectile, which cannot penetrate even with Deception of Dreeg Set. I know it from this topic - Dreeg’s Evil Eye transmuter doesn’t work with passthrough
