card idea: aus nec action

Army of Rats is not stackable. I don't know why you keep mentioning Shambling Hordes and Nucturn -- are you confusing minion card with ally? Many, many decks have a minion card that they intend to play frequently.

If the card is too weak (which I don't think it is, but maybe) the "tap to" could be taken off. If it's still too weak (which it probably wouldn't be), make the double superior burn two pool. If it's STILL too weak, make minions without Necromancy have -1 stealth on the action to burn the card.

Because those cards are played in double digits quantity ?

You are right: Army of Rats is a good card indeed. But that doesn't mean this card is crap at all.

Many tournament decks play many copies of one card. Look at cards like Deep Song, Govern the Unaligned, Bum's Rush, Kine Resources Contested, Psyche!, Kindred Spirits, Freak Drive, etc. It could be nice to have a weapon against such much focused decks.

But it's not a weapon. Most of those not play those cards at least once between your untap, and you can't play this card if they didn't played this card yet. It's not a weapon against those decks, it in most cases didn't hurt them more than single trochomancy (bleed for 3).

Army of Rats is not that good. This card is crap as you waste an action, card slot to maybe deal 2 damage over the course of game, if you are lucky. It's very easy to burn and don't deal much damage. It have no saving grace.

Weapon against such focused decks might be some event that activate if player have X same cards in his ash heap, and say deal 2 pool damage to such player (it didn't hurt recursion, but can hurt weenie ani spam or other one trick pony).

Something that can work would be:
Spectral Surveillance

+1 stealth action. Burn every other Spectral Surveillance you control.
Put this card in play and choose a minion card from your prey's ash heap to put on this card. When a minion controlled by your prey plays another copy of the chosen card (even if it is canceled) you may tap this card to cause your prey to burn two pool. Any minion may burn this card as a action. Minions without necromancy must burn 1 to attemp this action.
As above, and if the action is successful this acting vampire untaps at the end of the minion phase.

your idea's terrible!
it should be at least 10 pool damage when you tap it.
maybe 15.

Molloy wrote:

Spectral Surveillance

If this acting vampire is a Harbinger of Skulls the action is at +1 stealth.
Put this card in play and choose a minion card from your prey's ash heap to put on this card. When a minion controlled by your prey plays another copy of the chosen card (even if it is canceled) you may tap this card to cause your prey to burn one pool. Any minion may burn this card as a action.
As above, and if the action is successful this acting vampire untaps at the end of the minion phase.

Not strong enough to be playable. Too many conditions and even when it works your prey always gets to choose the lesser of two evils. Either remove the burn clause or attach a cost to attempting to burn the card, as suggested by Lech. With some kind of improvements, one or two copies might be a staple for HoS-decks but there shouldn't be any danger of this getting abused.