Hello,
Noob question, both this skills have “Reduced targets def. ability” it is stacking or not ?
Thx for answer.
No
In case of reduced the highest one applies
“-X% resistance” on the other hand stacks
it isn’t only for resist reduction then ? always wondered but never knew, so thanks for enlightening us 
Well, if you have 25 Reduced target’s resistances and 35 reduced target’s resistances. Then they won’t stack, 35 reduced target’s resistances will apply.
While if you have -35% All Resistances and -75% All Resistances, then they’d stack.
Also, your welcome
cheat sheet for resistances
Yeah, the wording holds true for all* stats. Including but not limited to slows, resistances, OA/DA debuffs.
*I shouldn’t make such sweeping statements as I actually only know it holds true for the examples I listed…but I’m fairly confident in this situation