Relative copy and paste in vim:

https://ptc-it.de/relative-copy-paste-in-vim/

tl;dr

:t is an alias for :co[py] and can be used in command mode like so

:-12t.<cr>

This will copy 12 lines above the cursor and paste on the current line it also works with different destinations (:-12t+19<cr>) and ranges

:3t9 - copy line 3 to line 9. Reads 3 to 9.

:3t. - copy line 3 to the current line.