FUN

FUN is a hidden value in each AUs code. As explained in Underplayer, different AUs have different FUN values. The higher the FUN value, the more evil the AU. After you get to 7 evil Prefixes and/or Suffixes, you reach the code's integer limit in FUN. After that, it overflows to Infinity in something called a "Reality Overflow". This makes the AU pure evil causing the evilness to consume the entirety of the AU leaving nothing but a void. As such, these AUs are completely unstable and never last more than a few seconds after creation. The lower the FUN value, the more benevolent the AU. If the you get past 7 good Prefixes and/or Suffixes, the FUN value is equal to the code's limit on the negative side instead of the positive side. If you go past that, it underflows to -Infinity (Negative Infinity) causing the benevolence to consume the entire AU, similarly to with Reality Overflow. This is called "Reality Underflow". These AUs are equally unstable. However, if they were to merge, they would form a neutral AU with a FUN value of 0 making it identical to Undertale.