For slayer marks i think you should progress it through stages kinda like tanjiro did. (Just a rough idea)
Ps: (Idk much about stats in this game so the stat buffs should just be what the devs want)
-1 initial mark) it could look like the jagged mark tanjirou had during the middle of demon slayer
-2 advanced mark ) this mark would look like tanjirous completed mark with the top of it looking like flames( or any other elements). This could give a slight buff to your base form without activation and with activation the mark could glow giving a bigger boost in power
-3 mastered mark) this mark could look like yoruiichis mark with both the top and bottom parts of the mark being shown. And upon activation the mark would glow and you could gain aura of your elemental breathing style
biggabuncheez You’ve Reached Level 3