Game Mechanisms
The rules for Chaos Cards is similar to, but with certain adaptations to accommodate our research focus. For game mechanisms, we focus on the process of the main adversarial gaming part where decks of cards are played against each other (called matches, to disambiguate from the general term, games), i.e. not focusing on card collection system etc. The key game mechanisms are as follows (cyan parts indicate major difference from Hearthstone, green parts indicates new mechanisms):
Each match is played between two players using their decks containing 20 cards each.
Each player starts with a leader with 30 hit points (HP), and the objective of a match is to reduce the HP of the opponent leader to 0 or below (i.e. destroy the opponent leader), or to win by special match winning effects.
The two players take their turns in alternating fashion. Each player starts with 3 cards from the deck initially at the hand (only cards at the hand are playable), and draw a card at the beginning of the player's own turn from the remaining card of the deck (during a match, the set of remaining cards yet to be drawn is referred to as the deck).
When a player attempts to draw a card when the deck is empty (i.e. all remaining cards are drawn), the player's leader suffers an amount of damage. This is called the fatigue mechanism. The fatigue damage amount starts from 1 and gets incremented by 1 for each subsequent instance in the same match, and the counter is separate for each player.
Whether a card can be played is mainly controlled by a resource called mana. Each card has a mana cost and each player has a pool of mana points (MP) to use each turn. A card may be played only if the player's remaining MP is no less than the card's mana cost. Each player starts with 0 maximum MP at the beginning of a match. At the start of a player's turn, the player's maximum MP is increased by 1 and all MP used in the previous turn is restored.
There are three main types of cards in Chaos Card: leader cards, minion cards, and spell cards. Playing a leader card replace the leader with the card (replacing the attack and health) and trigger its battlecry effects if any, playing a minion card places the minion on the battle field and triggers its battlecry effects if any, playing a spell triggers its casting effect.
Played leaders and minions are considered characters on the field and they be commanded to attack an opponent character at the next turn after they are played (at the first turn they are in the sleeping state). Leaders and minions have extra numeric attributes in addition to their mana costs: damage, HP (also called health) and attack times (how many times can it attack each turn). When attacking a minion, both parties suffers the damage equal to the other's attack value. In other words, the minion being attacked performs a counter attack. Leaders do not perform counter attacks. Having an attack value of zero does not disallow attacking or counter attacking.
The battle field (field) can accommodate at most 7 minions from each side. If the field is full on one side, that player cannot play any additional minions until some room is made.
Each card may have one or more of 7 designed ability keywords that make them not behave in default fashion in certain occasions. The details about all ability keywords are as follows:
Charge: The character may attack immediately (i.e. does not have to wait for a turn) after being played, i.e. it does not have a sleeping state. This also apply to leaders (leaders also has to wait for a turn to attack by default).
Taunt: When Taunt characters exist for one player, the other player cannot attack non-Taunt characters. Leaders may have Taunt. The Taunt ability is temporarily disabled when the character also has the Stealth ability (below), though the Taunt keyword is still on it in that case.
Stealth: A Stealth character may not be specified by the opponent as the target for attacking, playing targeted battlecries, or playing targeted spells. Leaders may not have Stealth. When a Stealth minion attacks, it loses the Stealth ability (as well as the keyword). A player may target allied Stealth characters with targeted battlecries and targeted spells. Stealth disables the Taunt ability temporarily without removing the Taunt keyword.
Untargetable: An Untargetable character or card may not be specified as the target by any targeted battlecries or targeted spells, even including those from the owner of the character or card. When considering it for a card, as opposed to a character, it means you cannot target the card at your own hand, which is often a compromise but can also prevent negative targeted effects being forced on it. An Untargetable character may be attacked though.
Shielded (Divine Shield): A Shielded character is immune to the next instance of non-zero damage (the shield as well as the keyword is consumed in the process), the Poisonous ability (below) from the damage source is also blocked by the shield and consumes it (even when damage value is zero).
Poisonous: Any damage from a poisonous character or card destroys the target if it is a minion and is not Shielded, even if the damage amount is zero. If the target is Shielded (no matter a minion or a leader), the shield will be consumed.
Lifesteal: Any damage from a Lifesteal character or card heals allied leader, by an amount that is equal to the actual amount of damage. If the damage is blocked by a Shield, then it is not regarded as an actual instance of damage thus does not trigger the healing.
A leader or minion card may also have special effects, which gets triggered at certain timing. Examples includes battlecries, which get triggered when playing those types of cards, and deathrattles, which get triggered when a minion is destroyed. A spell card must have special effects (e.g. spell casting effects), as spells does not persist on the field after being played, unlike leaders and minions. Effects that are triggered when playing a card (battlecries and spell casting effects) may require specifying a target, in which case we call them targeted battlecries and targeted spells.
The impacts of effects are diverse, including dealing damage to a character, modifying the mana costs of cards, and drawing cards etc. Triggering an effect may need other requirements (conditions) than the trigger timing, such as requiring the health of the minion triggering the effects (the effect source) to be lower than a certain value.
For targeted battlecries and spells, the requirements on the target is treated specially (compared to other type of conditions for effects), they are more like constraints rather than conditions. If there are valid targets (satisfying the requirement), one of them must be selected if the card (with a targeted battlecry or spell casting effect) is to be played. If there is no valid targets, minion/leader and spell cards follows a slightly different rule. A minion or leader with a a targeted battlecry effect, in that case, may still be played (assuming the field is not full for the minion case) but that battlecry effect would be ignored and the card will be treated as if it is untargeted. A targeted spell, in that case, may not be played at all.
Minions take one of the three minion types: beast, dragon, and demon. They are not associated with particularly different semantics currently, but are used in conditions for special effects (e.g. deal damage to beasts).
The term discard (as an effect or a triggering situation for effects) in Chaos Cards refers to not only the regular meaning of discard cards in Hearthstone, but also a wider range of situations. A minion on the field can also be discarded, which makes the minion exit the field, similar to being destroyed but without having its deathrattles triggered (but will instead trigger its on-discard effect if applicable). Cards deleted when adding to a full hand, and minions removed when adding to a full field also counts as discard events.
The second player gets a special 0 mana cost spell card initially at hand, as a designer balancing compensation. The card's casting effects are "reduce the cost of a card at your hand by 1" and "draw a card". We do not adopt exactly Hearthstone's counterpart second player compensation (get a 0 mana cost spell of "increase MP and max MP by 1 for this turn only", and get an extra card from the deck on to the hand at the beginning of match) as the mechanism of "this turn only" is not encoded in the card effect structure, although our version is a close re-design.
A match ends when one player loses (having leader destroyed, or the other player wins by special winning effects), or both players finish their 30th turn without losing, in which case it is a draw (a draw can also be achieved earlier if both player lose simultaneously). The turn limit is added in addition to the fatigue mechanism to help prevent prolonged matches, as certain special effects may add cards to the deck preventing fatigue from occurring.
Overheat is introduced as an advanced mechanism in chaos card that prevents the same effects from being triggered too many times in a pair of turns. In Chaos Cards, all copies of the same effect coming from the same source (with card copying, granting effects), called duplicates, are treated as the same effect in the overheat mechanism. Each trigger (when the condition part passed) of an effect increases its overheat count by 1 and by default the overheat threshold is 10 which, if reached by the overheat count, prevents further triggering of the same effect until the count resets. Unlike the consumed attack times, which reset at the start of the owner's turn, overheat counts reset (set to zero) at the end of the owner's turn. There are effects directly setting every effect on characters/cards to overheat (by raise its overheat count to max), which achieves the effect of temporary silencing (there's no exact mechanism in chaos card for silencing like in Hearthstone, but different aspect of it are included in different effects in Chaos Cards). There are also effects reducing overheat threshold on every effect on characters/cards which achieves the effect of persistent constraining or silencing (when the threshold is reduced to zero; note the count automatically resets but the threshold does not). There are no effects reducing overheat counter or raising overheat threshold (there are effects resetting the threshold back to 10 though). If an effects sets reduces the overheat threshold on multiple duplicates of the same effects, the reduction will be multiplied by the number of duplicates (e.g. if an effect reduces the overheat threshold on all enemy minions by 2, and there are three duplicates of the same effects on enemy minions, that effect will suffer -6 on its overheat threshold). The overall role of this mechanism is to help bound the length and actions and turns in Chaos Cards.
Any card/character copy/movement (take control/give up control/summon to field/put back to hand/draw from deck/shuffle back to deck etc.) preserves all states of the card, with very few excluded parts (sleeping state is re-evaluated when a character gets to the field in any form according to whether it has Charge ability, consumed attack times are also reset in those occasions).