Must needs.

[Vagrant-0]

Stated plainly throughout several end cutscenes, even spoken clearly by voice actors who despite being apparently fluent with the language apparently couldn't be bothered pointing out this grammatical flaw.

First instance is on airship spoken by Alphinaud just after the Garuda fight.
"But first we must needs find out all we can." Both the text and spoken line are wrong.

Several cutscenes after that point also have this same combination of words.

[HiirNoivl]

Needs is being used as an adverb.

We don't use "needs" as an adverb any more, but people used to. The word "needs" has been replaced with "necessarily".

So you can read that sentence as "But first we must necessarily find out all we can."

[Conradus]

Needs is being used as an adverb.

We don't use "needs" as an adverb any more, but people used to. The word "needs" has been replaced with "necessarily".

So you can read that sentence as "But first we must necessarily find out all we can."

Hiir is correct. "Must needs" may be unfamiliar to you, and it may be somewhat archaic, but it is perfectly correct and, indeed, well suited to the tone they are trying to create.

"And he must needs go through Samaria." --John 4:4, King James Version

Clown: My poor body, madam, requires it: I am driven on by the flesh; and he must needs go that the devil drives. --All's Well That Ends Well, Act I, Scene III

[Nialle]

FFXIV's archaic English trips up yet another player.

[Inzoum]

Joke's on the OP, I guess...

A lot of people have made the mistake of believing this is actually a mistake. Hiir is correct, and this was also confirmed by the localization team previously. This particular form is actually used by a lot of character, both by main story characters and generic NPCs