Multiple effects will apply separately, one after another, in the order they are listed on the item/skill.
Note that the attack state is applied exclusively via the
Add State: Normal Attack skill/item effect. This is present by default on the Attack skill. It comes with a percentage, e.g. 100%, that multiplies the attack state chance.
Example:
- A battler has an Attack State: Poison +20% trait.
They use a skill with Add State: Normal Attack 50% and Add State: Poison 80% effects.
Their target has an overall state rate of 70% for Poison.
- Normal Attack state: 50% * 20% * 70% = 7% chance of applying Poison.
Poison state: 80% * 70% = 56% chance of applying Poison.
As noted, these are rolled separately: the target might get poisoned 0, 1, or 2 times.
Edit: also, by default when a state is applied its duration is reset, so applying the same state 1+ times in the same action is pretty much the same as applying it once.