In this question I will talk about programs as strings, this is strings of bytes, not characters. How your resultant program is rendered or displayed is not important to this challenge, only how it appears in memory matters.
A pristine program is a program \$S\$ that when run does not error, however it will error whenever a continuous substring of size \$n\$, where \$1\leq n < \left|S\right|\$, is removed.
A filthy program is the opposite, it is a program \$S\$ that when run does error, however whenever a continuous substring of size \$n\$, where \$1\leq n < \left|S\right|\$, is removed, it does not error.
For this challenge an error is non-empty output to STDERR.
Your challenge is to write a filthy program that uses as many unique bytes as possible. This means you will get one point for every unique byte that appears in your code with a larger score being better. The maximum score is thus 256.