Makima could kill Gudao, Mash, and every servant they have in Chaldea. Her contract makes it so that she is always immortal and undamaged so as long as there is a Japanese personality alive. And her mind control ability lets her bind anyone she deems inferior to her to her will, forcing them to fight and die for her.
She would walk into Chaldea, immediately force all of the servants to kill themselves, and then murder Gudao before he could even react.