Since Sothe is a theif, maybe give him a sort of item-stealing move. Either his standard B or maybe his runnign attack. Like He runs forards and moves his hands in a quick grabbing motion. if he hits the opponent it does minimal damage, but if they are holding an item (beam sword, Pokeball, ect.), Sothe takes it and holds it instead. Obviously doesn't work if he's already holding an item, but reveryone's running attack changes with an item anyway so it works. Maybe this concept could work with his grab. If he grabs you then throws you, he takes whatever you're holding. And whatever way it is, it does very little damage if they aren't holding anything.
But I like the idea of Lyn because she was an AT in Brawl. She has a background in the Smash games beyond being just a trophy or sticker. What was one of the main reason we brought back Pichu over the hundreds of other possible pokemon we could have used? Because he was in Melee. I know he was playable and Lyn wasn't, but surely being an AT at least proves that she works well in Smash.
But I like the idea of Lyn because she was an AT in Brawl. She has a background in the Smash games beyond being just a trophy or sticker. What was one of the main reason we brought back Pichu over the hundreds of other possible pokemon we could have used? Because he was in Melee. I know he was playable and Lyn wasn't, but surely being an AT at least proves that she works well in Smash.