In a certain code, MASTER is written as TBNSFU. How will DANCER be written in that code?

Let's split the word $\text{MASTER}$ into two equal halves of three letters each: $\text{MAS}$ and $\text{TER}$.
1. For the first half ($\text{MAS}$): Increase each letter by $+1$ and then reverse their internal order:

$$\text{M}(+1)=\text{N},\text{A}(+1)=\text{B},\text{S}(+1)=\text{T}\to \text{N B T}\stackrel{\text{Reverse}}{\to }\text{T B N}$$

2. For the second half ($\text{TER}$): Increase each letter by $+1$ and then reverse their internal order:

$$\text{T}(+1)=\text{U},\text{E}(+1)=\text{F},\text{R}(+1)=\text{S}\to \text{U F S}\stackrel{\text{Reverse}}{\to }\text{S F U}$$

Combining both modified parts gives $\text{TBNSFU}$.

Now, let's follow the same operation for $\text{DANCER}$ ($\text{DAN}$ and $\text{CER}$):

1. First half ($\text{DAN}$):

$$\text{D}(+1)=\text{E},\text{A}(+1)=\text{B},\text{N}(+1)=\text{O}\to \text{E B O}\stackrel{\text{Reverse}}{\to }\text{O B E}$$

2. Second half ($\text{CER}$):

$$\text{C}(+1)=\text{D},\text{E}(+1)=\text{F},\text{R}(+1)=\text{S}\to \text{D F S}\stackrel{\text{Reverse}}{\to }\text{S F D}$$

Combining both halves yields $\text{OBESFD}$.