Suppose you have the following input file: 
a 123 456 789
b 123 456 789

c 123 456 789
d 123 456 789

<p>e 123 456 789
f 123 456 789</p>

<p>e 123 456 789
f 123 456 789
g 123 456 789
h 123 456 789</p>

<p>1 123 456 789
2 123 456 789

3 123 456 789
4 123 456 789</p>

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The following matches the last three paragraphs:
perl -p0e 's/(<p>(?:(?!<\/p>).)*<\/p>)/-->$1<--/migs' example.txt

You want to change the regex, to match the third paragraph only, because it contains an empty line.

Hint: the following does not work
perl -p0e 's/(<p>(?:(?!((<\/p>|\n\n))).)*<\/p>)/-->$1<--/migs' example.txt

In reply to regex exercise by Cilice

Title:
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