The Archer Gilden Silveric is an awesome early Hero. He's a fierce defender and it wouldn't be an exaggeration to say he's saved the day in many of my games. If someone asked me for one thing about Ljosalfars, I might say, "Recruit Gilden ASAP"
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Gilden Silveric can be a fantastic attacker if the stage isn't two late (i.e. few T3 or T4 units).
Indeed. I just started playing FfH (and am currently taking a self-enforced break from it, because it's sucking up ALL my time

and I do have bills to pay...), so I'm still on Noble difficulty. Perhaps things change at higher difficulty settings, but let me tell you about my current game to illustrate how powerful Gilden can be.
I forget which map I started my Ljosalfar game on (I think it was the "Huge pre-settled 21civs map", but I'm not 100% certain), but I ended up starting on the east coast of the world's major continent, in a heavily forested area (with some jungle to the south of me). My neighbors to the north were the Svartalfar, also in a heavily forested area.
I know little yet about how to play each civ, but I do know that the elves don't want to chop down forests. So I beelined for Archery to get lumbermills, and started placing lumbermills near all my cities. Then I noticed that my hero unit was already available to build, so I built Gilden in a northern city, near the Svartalfar border. (That particular city had been placed to create said border, limiting the Svart ability to expand southwards. Open Borders? Why in the world would I want to sign an Open Borders agreement with the civ that most directly competes with me for the type of land I want?).
After building Gilden, I decided to test out his power. So once he'd sat around for a few turns gaining XP, I declared war on the Svartalfar, gave Gilden Shock and Cover, and sent him north along with a couple of archers to test the Svart defenses. To my surprise, the Svartalfar had nothing but warriors in their cities, and most of their culture defenses were only 10% or so. (I think their capital was up to 30%). With Shock, Gilden's attack chance was above 95%, as long as I avoided crossing rivers in the process -- and double-move though forests made that easy. The archers ended up being used only to garrison each city as I took it; Gilden did all the killing.
Faeryl was building new warriors as fast as she could to replace the ones I was killing -- I'd see a new warrior show up every few turns, and while I attacked the Svart capital I intercepted the occasional warrior moving to reinforce it from another town. But Gilden was killing one unit per turn, and Faeryl couldn't build new warriors fast enough. He did take damage every once in a while, but I simply used Combat promotions to heal him most of the way to full (which simultaneously made it much less likely that he'd get damaged in the next fight). Once the capital fell, it was pretty much all mop-up from there, since at that point Gilden had two or three Combat promotions and a >99.9% attack chance. In the end, Gilden Silveric
single-handedly wiped out the entire Svartalfar civilization, and was still at 95 HP when the fighting was over.
If you get Gilden early enough before your neighbor has started building archers, he can be
devastatingly powerful.