The Hoard gives 1 gold, 1 gems, and the Enchanted Blade promotion. It used to 1 Mithril instead of the promotion, and lore entries do indicate that dragons really like collecting mithril. (They collected enough for the dwarves to be able to convince humans that mithril was actually dragon bone, so they could laugh at them foolishly going of to their deaths, or if they are lucky to slaying the beast that stole the mithril from the dwarves, who would then claim it back.) It was changed because once the Mithril Weapons promotion no longer required a specific building the barbs and whoever captured Acheron's city got a huge advantage in the early game.
(In my version, the Hoard is back to providing Mithril again, but the Mithrl Weapons promotion has a tech prereq. (My Mines of Galdur also provide 2 Iron, Gold, and Mithril instead of 3 iron.) Since Dragons in my version are Nukes and cannot be built until the Stir from Slumber ritual awakens them, I changed it so tat The Hoard spawns Acheron instead of the other way around. I forgot to make this wonder barbarian only, and don't think I will as letting players choose to let a barbarian dragon steal their city seem cool. I did of course remember to only make Acheron spawn this way once, not every time the equipment is dropped. Oh, Acheron has 3 movement too (and 36 strength, blitz, etc), but so long as he is in a city with his hoard he will have a promotion making him immobile. Stealing the hoard will make him wonder free until he can settle down with his riches again in a new city.)