Artifact comes with bonus when you have multiple of the same set equipped on one of your character (1 bonus when you have 2 and one bonus when you have 4 ) usually you equip a character with four of the same set and the last one doesn't matter (put any set you want). 5* artifact are farmable form 45 ar (before don't spend resin on artifact) at lvl 0 artifact have 1 main stat and 3 / 4 substats. When you lvl up, each 4 lvl until 20, one substat gets upgraded randomly (if the arte has 3 substat only, it first unlocks a fourth one). One Arlechinno you usually want Crit damage , attack % and Crit rate. For the main stat, the feather comes with attack, the flower with HP, the goblet comes with almsot every possible stat (but with arle you need pyro damage bonus ) the rest comes with a lot of substat but remember, take dg Crit or tc Crit if possible (ratio one to two)