Surprise Party for Brain-Flak
Python 2, 39 37 36 34 bytes

-1 thanks to dzaima

-2 thanks to Erik the Outgolfer



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Try it online!

Relevant characters:

exec"".joinchrlenxforxin''.split""


Explanation

This program builds the string:

print"Surprise!\nHappy Birthday, Brain-Flak!"


It does this by converting a long string of parentheses into character codes.  Once the string is built it executes it.

It builds the string with the skeleton:

"".join([chr(len(x))for(x)in'&lt;...&gt;'.split("{}")]))


This splits the string along {} and maps each section to the character code corresponding to its length.  We can then build the entire string out of parens for a cost of zero bytes.