Young Link was not Young Link in terms of what you expected. Both his designs and new specials come from his A Link Between Worlds incarnation. His specials would be based around his rods (Fire, Ice, Sand, Tornado). Some of his moves are similar to the other Links (D-Air from what I can remember), but his spin attack is his D-Smash because I believe the Tornado Rod was his new recovery and his F-Smash was changed to the Hammer. Finally, I think his dash was changed into a rolling attack where he rolls into you like he's a bowling ball. I remember him most of all from the dream.
Then there's Retro Link. I can't remember much besides that his recovery was just a high jump followed by a large stab. I do know that he uses his spells from Adventure of Link (which is also his Link design) and some items from the first Zelda such as the Magical Rod or the Bombs where he places them instead of being able to throw them. He can also detonate them at will like Snake's C4 attack.
Finally, there's Dark Link. He was basically the trickster one. He has a boomerang (I think the design was similar to the one in ALttP) that sends the opponent near Dark Link. But what makes him different is that unlike the others, he uses the Biggoron Sword and his shield is on the back of him. However, the shield is still active, so if Dark Link is facing away from you and you throw a projectile at him, the shield will block it. His F-Smash is reminiscent of
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's F-Smash in Smash 64. His other specials are essentially magic moves that could've been used if
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was given his own moveset via Dead Man's Volley and others.