I didn't mean "Stock: -10 instead of Enemy Stock: +10 (or 12 now)" but instead "Stock: -10 and
Enemy Stock: +10", for a total difference of 60 resources between you and your opponent (or more like 45-50 with good timing), putting this card closer to the strength of those summoned by Wishing lagoon
... or, with your tweaks, about 3-4 Scepters of Summoning
in a single turn, except much easier to play either way.
Those tweaks confirm the card as overpowered; since not only does it summon from your deck, but also doesn't scramble the rares already in hand, that means you can safely combine it with cards like Death Prophet
and Magic Lamp
— and as you said, Wealth
and Fair Trade
— to get an incredibly powerful deck, right up there with old Brigand, Tower-kill, or Sabotage+tower-building.
Hm, to weaken the combination with Death Prophet/Magic Lamp, how about instead of giving it "Stock: -10", you can make it cost 30 gems? That satisfies the 60 resource difference for the strength of the card, and also make it less likely to get used with Catastrophe
On the comparison with Necromancy Amplifier
, it costs 2 stock more than you remember, and has the caveat of locking you into an Undead deck; the other undead cards have costs, balances, and problems with Holy decks to balance out getting a relatively cheap and strong uncommon card.
I suspect your comparison for Danai present is based on your experience with your much-used Farsight deck, and non-hidden games; it's a lot less useful when you don't know what you're making the opponent lose and don't know what you're giving them... and even when you do know, there are some Uncommon 0-cost cards that can do you more harm than good— in addition to the stock they get.
Edit: If you make that rare card, I recommend calling it "Heroism", and letting it keep the Stock+ for both players. Makes it like a version of Enlightenment for hands and stock instead of facilities and tower.