[Shadow5YA]

Originally Posted by shadow1296

just saw another extra boss and its

Spoiler for extra boss:

fsn archer and his master tohsaka rin he fights the similar if to his extra version but his attacks are more powerful

I have felling that all the original extra servants all optional boss fights and the last one will probably be everyone favorite saber, auturia

Actually, the only confirmed optional bosses so far are

Spoiler:

Kotomine and Lancer from F/SN, Rin and Archer from F/SN, and Twice and Caster.