On that one hidden move called the 'backslice', I've tried SO many times..

This move is actually very easy once you get used to it. There isn't any trick you're missing. It's actually just performing two old moves you already perfected, but connecting them together as one combo attack. The back-slice is basically you Z-targetting an enemy, side-stepping twice to the left or right, and then shaking the Wii Remote. What this does is enabling Link to target an enemy, circle the enemy to the back, and then quickly ambushing it from the back before it has a chance to attack. Just press Z to target the enemy; tilt the control stick left or right, then press Z slightly, before pressing A (so left/right, Z, A); and then repeat this before quickly finishing it off with a regular sword attack (shaking the Wii Remote). It takes a couple tries but you'll do it right eventually.