[TxMt] Matching multiple lines in a grammar pattern

Hi all, I'm trying to add an invalid scope to a certain group of lines. Basically, the regex pattern I would like to match is this:

^(\n){2,}

Which works fine in the Find dialog, but when trying to use it as a pattern, it doesn't work. I am guessing because of the way that the pattern matching works for grammars, but is there a way to match this?

The logic is, I would like to match every line that has no content on it, but is part of a group of 2 or more extraneous lines. One \n is valid, but 2 or more is invalid.

I've tried so many variations of trying to use captures, matching content, but it seems to be treating each line as it's own match independent of the previous or next ones.

Anyone know how I might go about applying this?

Any help is greatly appreciated.

Thanks!