In a certain code language, VEGETABLE is written as FMCBUFHFW. How is ARSENAL written in that code language?

Let's find the logic behind coding VEGETABLE to FMCBUFHFW:
If we write the word VEGETABLE in completely reverse order, it becomes: ELBATAGEV.
Now, shift each letter of this reversed word forward by $+1$:

* E (+1) $\to$ F
* L (+1) $\to$ M
* B (+1) $\to$ C
* A (+1) $\to$ B
* T (+1) $\to$ U
* A (+1) $\to$ F (Wait, let's verify direct correlation from the last letter: V+1=W, E+1=F, G+1=H, E+1=F, T+1=U, A+1=B, B+1=C, L+1=M, E+1=F)
So, the correct pattern is: Reverse the entire word and add $+1$ to each letter.

Reversing ARSENAL gives: LANESRA.
Now, add $+1$ to each letter:

* L (+1) $\to$ M
* A (+1) $\to$ B
* N (+1) $\to$ O
* E (+1) $\to$ F
* S (+1) $\to$ T
* R (+1) $\to$ S
* A (+1) $\to$ B

Thus, the code is MBOFTSB.