List of cards that are hard to implement

Question

What are some examples of cards that are likely hard to implement?

Only one or a few tightly-coupled cards per answer (if the difficulty comes from the combination of the cards), please.

Up-vote any answers if you'd like us to support the mechanics from the cards.

Answer 1

Card: Baron Rivendare (Hearthstone)

Problem: "Your minions trigger their Deathrattle twice"

What's so difficult?

This card changes one of the core mechanics of the game. Normally each minion only dies once, you could say that this card however makes the minion die twice. It needs to listen for a minion dies event and execute a new such event, without causing an infinite StackOverflow loop.

Idea on how to possibly implement:

To be announced

Answer 2

Card: Archetype of Finality (MTG)

Problem: "Creatures your opponents control lose deathtouch and can't have or gain deathtouch."

What's so difficult?

This card prevents opponent creatures of having or gaining the Deathtouch ability as long as this card is in play.

Idea on how to possibly implement:

No idea

Comments

Effects on cards could be stored in components. If this was the case you could simply `disable()` a component.

Answer 3

Card: Auchenai Soulpriest (Hearthstone)

Problem: "Your cards and powers that restore health now deals damage instead"

What's so difficult?

This is yet another one of those cards that alters the behavior of other cards.

Idea on how to possibly implement:

When this card is in play, listen for a HealthRestoredEvent (or HealEvent), check if the source of the healing is from the same player as controls this cards, if it is then cancel that event and deal damage instead.

Answer 4

Stalagg, Fuegen and Thaddius (Hearthstone)

Ability: Deathrattle: If Fuegan also died this game, summon Thaddius.

Ability: Deathrattle: If Stalagg also died this game, summon Thaddius.

When both of these two cards die in same the game (on either side)  it immediately summons an 11/11 unit with no ability. Imagine the possiblities when combined with Faceless Manipulator which makes a copy of a card. Also consider the legendary that causes units to fire their Deathrattle twice, and the Shaman card that resummons a minion after it dies. A counter would be any card that silences or converts this to another unit (such as Hex). If both players are playing these two cards, quite a few of the 11/11s can be summoned in one game.

I definitely can't think of an easy way to implement this without a special boolean flag.  A better system would allow for easily adding more of these without adding more bools to keep track of.

Answer 5

Card: Eching Ooze (Hearthstone) http://hearthstone.gamepedia.com/Echoing_Ooze

Ability: Battlecry: Summon an exact copy of this minion at the end of the turn.

This might not seem like a difficult card to code on the surface, but the way they implemented it demonstrates some complexity.  

If you modify this card during the turn it is played, those buffs are applied to the copy that is created at the end of the turn.  This includes buffs provided by other minions such as Divine Shield or +1/+1.  However, if a buff is appiled that says something like "Add +2 attack until end of turn", even though the copy that is made at the end of the turn might be a 3/2, the buff is still removed from the copy at the end of the turn.

I was not sure how this would behave until I played with the card, and they clearly had to make a choice about how to do it.  I think that based on the wording of the card, the buff might have stayed on the minion after the end of the turn, regardless of what it said on the card that casted the buff. I guess it depends on how you define "Exact Copy", and also on how they impemented those buffs themselves.

Comments

The temporary buffs are not that hard to implement, I have managed to do that in my HS code (it was a challenge at first though). Copying cards however can be quite a challenge, especially with these enchantments attached to it! (I have not fully implemented copying cards in my HS code)