The Phantom Hourglass & Spirit Tracks Pack brings another set of 12 multi-elemental weapons to Hyrule Warriors: Legends. Windywalk has compiled a list on GameFAQs with all the new ones:
I'm really happy that Twili Midna got Light as the second element for the Mirror. It's the most powerful combination, since a majority of the ingame characters are weak to either element, which is probably why it's the only dual-element weapon of that type. It also makes fully sense for the Mirror, because it already combines Light and Darkness attacks. However, I still was afraid that she might get something else, like Darkness and Water, because you can never know with Koei Tecmo. After all they gave Agitha the Fire element, while her Parasol always was a Light and Lightning combo.
Cia did get the Lightning element and I'm good with that, because it's also a quite useful element and it fits her character and weapon type quite well. I'm not opposed to any of the new combinations, though some of them seem a bit random and some element combinations are already overused.
Right now we have 24 of the original 35 non-DLC weapon types with dual elements and there are ten possible element combinations. With 35 weapon types you'd expect that each element combination will get three or four weapons. But it doesn't seem like it will be that balanced in the end, let's take a look at the current distribution:
There are already four Light+Water, Darkness+Fire and Fire+Lightning weapons, as well as three Darkness+Lightning weapons. Oh, well... And what weapon types are left?
Well, looks like Link will have lots to do on the final DLC Map... Also, these are all weapons from characters with multiple weapon options. It might be that they leave some of them out in case they really are adding a 30th character and already got his or hers weapon tiers on the map as goals. But that doesn't have to be the case, it's just notable that Link and Zelda will get the majority of 4+ weapons in the last pack.
In case of the Hylian Sword I would expect it to get Fire. The Spin Attack looks fiery in some 3D Zelda games and Light+Fire is a completely underused element combo so far. Crossbows could also get Light, so Linkle can shine more and finally fight Darkness as the Legendary Hero.
Light Sword and Rapier would probably give a good Light + Lightning combo, which is underused as well. But for Zelda a Light + Fire combination would also be interesting, because then she would have access to all elements. Lana and Link would both need Darkness to get there, but I doubt that they will give Link the Darkness element. At least with Lana there's a chance that she will get something like a "Dark Sorcery Book", which matches the elements of Cia's main weapon.
The Dominion Rod is the only other Light+Darkness combination that I could see happening here. I remember, how I complained about the Darkness elements of both the Mirror and the Dominion Rod, when the Twilight Princess DLC came out. And now Koei Tecmo can make up for this.
The Great Fairy will probably get "inflamed", because she already is using some fire attacks and the combination of Fire and Water so far. And Ganondorf will probably get something like "Swords of the Flood" for a water combo, so he has access to that element as well. Thematically the weapon itself should get Lightning as the secondary element, but he already has that with the Trident.