I was just thinking of playing some fun teams and stuff, when I remembered I might as well try some Windfolk teams. The idea about starting with 50% mana was tempting.
… When I realized, almost all Windfolk start with 50% mana already. Ragnagord, Nax, Blade Dancer… Faunessa starts at full mana, even.
… Why would they give King Silenus that trait?
They were fresh out of ideas I guess, unfortunately. So many missed opportunities…
I traited silenus then didn’t bother traiting nax. Weird design choice imo.
For now, the only thing legendary about Silenus traits is his impervious…
But I guess with new troops and maybe a wildfolk hero class, this trait could become usefull. Just not at the moment…
Rework! Rework! 
Do they stack together to become +100%?
They don’t. They rewrite each other. Meaning if you had Faunessa 2nd slot and Silenus 4th slot, your faunessa would actually start the battle with 50% mana only.
This was fixed some time ago. They still don’t stack, but you’ll no longer reduce the mana of an empowered troop with the 50% mana legendary traits.
Imagine how good this trait would be if the Wildfolk race was never split. I have no idea why they made a conscious decision to categorize the Wildfolk into a bunch of more specific categories, then months later put in a legendary trait that only applies to the ones that they failed to categorize.
Oh, I didn’t know that. I always purposefully avoided it because of the past.
… Looks like nuclear chemists can learn something new every day, too. 
Thanks for enlightening me!