Hi Lee,
Let’s say the composition you want to mirror is called COMP_1 and it has some text across the middle. Create a new comp called COMP_2. Drag COMP_1 into COMP_2 twice so you got two copies of COMP_1 in your new comp. Now twirl down the top COMP_1s scale modifier. Click on the little chain-link graphic which means you can now individually resize X and Y. Now simply make Y = -60. Leave X at 100. You’ll see if has flipped your composition AND squished it a bit. Now all you need to do is position it up and down a bit so the bottom and top meet. You can then set the top comp’s transparency to 75% to give it a more reflective look. Try also applying some wave effects if you want a watery look.
Good luck.
Alex
http://www.lightdrop.com.au