Duplicate or move whole lines to any address with one command.
4 drills
Copy the cursor line: Copy the cursor line to where the target has a second copy of it, with :t and a destination: . (just below), $ (the end) or 0 (the top).
Move the cursor line: Move the cursor line to where it is in the target with one :m: :m0 (top), :m$ (end), :m+1 (down one) or :m-2 (up one).
Fetch a line from elsewhere: The target has a copy of a line from higher up, just below the cursor. Copy it there with :{N}t. without moving the cursor.
Move or copy a selection: Select the cursor line and the one below it with Vj, then press : and finish the command (m0, m$ or t$) to put them where the target has them.