Didn't his contract with Mashu makes him resistant to mental attacks/debuffs?

Nanau3 said:

Didn't his contract with Mashu makes him resistant to mental attacks/debuffs?

Actually the protagonist has piss-poor resistance to mental attacks, which is why Servants with affinity for dreams like Dantes normally covers for them, it's not fullproof though since Servants like Abigail and Lady Avalon can still invade your dreamscape without permission.

Nanau3 said:

Didn't his contract with Mashu makes him resistant to mental attacks/debuffs?

Mostly curses and poisons. Fujimaru's mind gets kidnapped into Singularities so often the staff is already used to it.