Apr 30, 2020, 00:4704/30/20
Open your champion tab and click on random artefact. See that big stat on top on it and some small stats below? The big one is called "primary stat" and the smaller ones are "substats".
Both of them can be flat number or percentage. For this mission you have to get from that exact stage gauntlets with big number that state ATK and is not flat, but percentage.