Catch Phrases tend to be seen as mary sueish or gary sueish but they don't have to be. Here are some cliches to avoid:
Saying a catchphrase similar or even the same thing as any other creepypasta: Avoid this at costs. There isn't any way to make this better.
Saying a catchphrase that are song lyrics: This only works if the oc is really into music or certain song. For example if the situation or the victim reminds the oc of a song then that isn't too bad. But if it has nothing to do with ocs, then no.
For a good catchphrase make it relate to the oc. For example if the oc is killing for revenge then maybe say something like: "It's time to pay the price..." or "Go to hell were you belong." You can also have multiple catch phrases as well. Like maybe the catchphrase will depend on the situation. Like if the victim is making a ton of noise when the oc is trying to not to attract attention they say something like "Shh...You'll wake them up." Or if it's day "Shut it. You'll alert others." Or maybe the oc doesn't need a catchphrase. Not every oc needs a catchphrase. For example if the oc is a silent killer then it doesn't need a catchphrase. Overall make the catch phrase or catch phrases relate to the oc.