(Note: No idea if this has been posted before, it probably has, but i'll roll with it the best i can)
I know that this isnt exactly cannon to the design of Zelda and my idea could be dependant on Zelda being a sage in any other zelda games ~
In The Legend of Zelda: Ocarina of Time, Princess Zelda was essentially THE Sage of Time. Taking this 'aspect' of her character, there could be a foundation for a final smash.
Much in the style of Peach, Zelda's final smash would not be brutally damaging persay. We all know Zelda is a slow character in terms of movement around the battlefield and keeping in theme the Sage of Time idea mine is this-
Zelda distorts the flow of time, slowing down the opponents and the environment around her (including items, hazards and any background animations. This has been proven possible on enemies with the stopwatch item, so it isnt completely out of the question)
This, in turn would help counter her slowness on the battlefield. Of course this might strike up issues of being a little
too similar to Peaches final smash, however the key difference would be that Zelda's is
completely inescapable, leaving Zelda free to pound into her opponents like theres no tomorrow, with little threat of serious retaliation.
Is it overpowered? HELL YEAH! (although this could be dependant on the duration of the time-distortion).
Extra Details: During the Final Smash, the environment's colour would be completely washed out, and set to greyscale, bar the characters themselves (this is a hint towards Hyrule at the bottom of the ocean in Legend of Zelda: The Wind Waker, helping to incorporate at least
something from Wind Waker).
Now during the final smash, theres the issue of knockback on attacks. This would be a double edged sword to help balance out the final smash. During this, Zelda's attacks would have NO KNOCKBACK whatsoever. Each attack would affect the enemy much like Fox's lazers in Melee.
This ensures that it will still require skill (regardless of how little) to finish the opponent after the smash's effects have worn off, as a KO could only be achieved then.
What would this mean for items? Same deal. Crates would be un-breakable, stopping Zelda from acquiring items from crates. As well as this, items would not be able to be picked up or caught, keeping in tune with the 'no items during your final smash' thing thats been popular in brawl (there are exceptions, but overall this seems to be a standard so far).
So sorry if this was a little big, i got carried away.