Some attack skills, rather than being manually activated, have a chance to trigger every time you make a standard attack (sometimes with restrictions such as only triggering if you're using a 2-handed weapon or a melee weapon).
If I invest in two different such skills, say the soldier's Markovian's Advantage skill and the shaman's Feral Hunger skill, so that each has a high chance of triggering, can a single default attack trigger both skills?
There's more than one kind of "triggered attack" (henceforth "proc") in Grim Dawn, and the answer to your question is different depending on which type you're talking about.
The first type of proc is Weapon Pool Skills, or WPS, like the Direwolf Claw skill granted by this item. These are modifiers to your autoattack (or to skills similar to your autoattack) that make it do something special on top of its normal "deal your weapon damage to one target" behavior. The procs mentioned in the question, Markovian's Advantage and Feral Hunger, are both WPS.
WPS are so-named because their chances to proc go into a probability "pool" and are drawn randomly from that distribution each time you attack. For instance, if you have two WPS, each with a 25% chance to be used, then 25% of the time you will use WPS 1, 25% of the time you will use WPS 2, and 50% of the time you will use no WPS. If your pool adds up to >100%, then the chances for each WPS to proc will be scaled down proportionally to "fit" into 100% (e.g., if you have 5 different WPS, each with 25% chance to be used, then their actual chance to proc will be 20% each).
You cannot trigger more than one WPS with a single attack; they are mutually exclusive.
You can recognize a WPS because it will always say "% Chance to be Used" in its description. This guide has detailed information about WPS and how they work.
Some items grant procs that are not WPS, like the Bear Claw skill granted by this item. These procs differ from WPS in the following ways:
There is no hard limit to the number of these that can proc at once; if you have 10 item-granted procs, then it's possible (though probably unlikely) for all 10 to proc at once off of the same hit. Item-granted procs can also be triggered by a hit that also triggers a WPS without any conflict.
There are some procs that are granted by the devotion tree (the constellations you invest points into by cleansing shrines throughout the game). For instance, the Aetherfire skill from the Imp constellation is listed with "15% Chance on Attack."
Devotion procs must be "bound" to a specific skill in order to trigger (you do this by clicking on the star that grants the proc in the devotions screen, which will bring up a menu of skills available for binding). Once bound, the devotion proc will have a chance to trigger each time the chosen skill hits an enemy. This chance is adjusted upward if the chosen skill has a cooldown, to make up for the fact that you can't use it as often.
Only one devotion proc can be bound to a given skill at any given time, so in general, a single hit from a skill will not trigger multiple devotion procs.
There's one possible exception to that rule: When a default attack replacer (DAR, like Savagery) procs a WPS (like Feral Hunger), the result is a single hit that combines the properties of both skills. If you have devotion procs bound to both the DAR and the WPS, the hit can probably trigger both devotion procs.
TL;DR: Each hit can trigger, at most:
Yes they can!
Not only that but they can also trigger spells you've unlocked with your devotion skill-tree.
A lot of auto-attack based builds actually rely on this method. You skill into multiple auras/passive effects and then you'll assign some strong devotion abilities to them.
While devotion abilities are still strong on passive auras you should keep in mind that they have a relatively low chance of activating when used on a passive effect.
I can really recommend stacking multiple passive auras with certain characters. It's insanely fun watching all the devotion spells trigger at once with a single auto attack. (Nothing beats volcanoes, meteorites and flame rings burning your enemies after you've smacked them with a hammer)
Okay, kinda a necro, but I will go indepth on this.
If a skill procs off default attacks and lists the chance in the attributes section rather than in the name, Only one can trigger. To add on to this, it can never go over 100% so if you have 5 25% skills, Each actually has a 20% chance. If you have 1 50% and 3 25%, the chances become 40%/20%/20%/20%.
If a skill has % On attack, then it can stack including with a second copy of itself in the case of rings.
no, they cant. its ether markovian or feral, cant be both at the same exact smack
