For some legendary skins, it appears that they give the hero both unique visuals and unique voice lines.
Some legendary skins I know off the top of my head that have different voice lines:
- Mercy Imp or Devil, upon reviving she says "Heroes never die! ... for a price."
- Hanzo Okami or Lone Wolf
- upon using Sonar he will sometimes say "See through the Wolf's eyes" instead of "See through the Dragon's eyes"
- upon Ult he says "Ryuu ga waga teki kurai" or something like that, and instead of 2 dragons flying out, 2 wolves fly out in the same formation
Besides the actual skins of the guns and player models being changed, are there other legendary skins which affect the ability appearances or the voice lines? I got my hands on a Vishkar Symmetra but it seems that, besides the model and the weapon being changed, I have not seen any unique voice lines or even unique ability animations or appearance changes.