One way u can do it is if when u do ur arcane art even if its still going hold the B
button thats the way i did it but if u still cant do it it dosnt rly do that much ur fine
witout it

it might be that you haven't gone under skill settings. go there for whatever character
you want, and search for special click on that.and it will inab;le you to use mysitic
arte.

you need the special skill and whe using a arcane arte dont use b pres a button and tada
mystic arte