Damage over Turn, based on user status value

Your status change's Change Value setting can do that directly via the Combatant > Status Value type. Just select the status value you want - the User game object is the combatant who cast the effect on the target, the Target is the combatant that has the effect applied.

Alternatively, you can use a formula in case you want to do something more complex :)

C) I'd like to create a Status Effect that modify the damage based on the ability type used.
Eg: Heal for 10% of physical damage received
Increase any physical damage abilities by 50%

i think i should use attack modifiers but i'm not getting anywhere...

A) it's not that, my ability has the same attack modifier attribute for each target changes.

B) awesome

C) in an ability, are target changes applied in order ? (eg : target change 0 then target change 1 then target change 2 ... )
because if it is i can't make it work.
i have an ability with :
target change 0 = trigger a status effect to target (status effect gives counter=100)
target change 1 = damage to hp
so the target should counter but he doesn't (but he will counter next damaging ability)

A) Hm, can you show me your setup (both flying text and ability status changes)?

C) Yes, the changes are made in the order they are defined.
I.e. target change 0 > status change 0, target change 0 > status change 1, target change 1 > status change 0, etc.
Counter would be calculated after all target changes, though. The issue is that the status effect being applied doesn't immediately add those status changes, as there's a 1 frame delay on the status recalculation to get all status changes combined (bad performance otherwise). One way around taht would be to have the counter chance use a formula that e.g. checks for such a counter effect being applied and give 100% chance in that case.

D) Depends on which schematic. The ability's schematics have access to them, naturally (that's where those actor types can be used, as stated in the help text for Actor Type).
Outside of an action's schematic, you can use selected data to achieve this. E.g. using a Select Combatant node, you can get the Last Target of a combatant.
Alternatively, you can also store the target(s) of an action into global selected data at the start of an action to have the latest targets available everywhere (also using Select Combatant node).

A) Hm, I'll do some tests.
Edit: Yep, it's a bug, will be fixed in the next update :)

C) Base counter chance is defined in Battles > Battle Systems > General Settings.
The formula just needs to check for that status effect, i.e. using a Check Status node and change the result based on that (e.g. Value node setting to 100).
Since counter is checked after the target changes, the effect is applied at that point and the formula can check for it.

D) Yeah, Individual Target is something different.
You just need to use the Combatant combatant origin and the Starting Object object - i.e. this uses the target of the action when used in the battle action#s schematic.