Mask change can not be active to face down drilldark
Gladiator beast can fusion summon use face down GB
So what is the keyword to know you can use face down moster to something or you must use face up monster ?
u just cant, deal with it
I cannot explain to you why contact-fuse or fusion can use face-down monsters; while you can't synchro face-down monsters. You know you can treat a face-down "Kaiser Sea Horse" as 2 tributes while "Skill Drain" is on the field? It is just pure rulings, game mechanics.
However for Mask change it activates by targeting a "HERO" monster, a face-down monster does not have a name.
Sure, you can try
Are you sure that Mask Change can not be used on a face-down Drilldark?