Okay I figured it out... you have to do the challenges in order, so after you beat the one between 9&10... beat 20 again to unlock one between 19&20... and do the same with the 30 to unlock the white completed tag.
Tienes que derrotar en menos de 10 turnos al nivel 10,20 y 30 y te saldran 3 niveles ocultos, para derrotar al de nivel 30 en menos de 10 turnos recomiendo buster blade
You have beat level 10, 20 and 30 within 8 or 10 turns to open up the hidden challenges. At least thats what i did and got the event complete trophy. hope this helps.
THANK YOU FOR THIS THREAD SECTION I JUST FOUND THIS INFORMATION 3 hours BEFORE EVENT ENDS - THANKS ALOT FOR TELLING ABOUT THE MYSTERY (and btw konami is serious hiding a title behind a secret smh!)
They hid the title behind the one people are likely to get randomly. (Even just autoing them, you'll likely eventually beat floor 30 in 10 turns.) Don't see a problem with that, personally.