The game of Undercards has many unique abilities that come in two forms: Abilities attached with monsters and Effect Cards.
Effect cards, also known as Spell Cards, don't require a spot on the board to be used. There are 82 Effect Cards currently in-game, 9 for each of the 7 classes and 19 others. The Effect cards for the classes are divided in 1 Basic, 3 Common, 3 Rare and 2 Epic in rarity (with one of the 3 Common Spells coming from DR, while all others coming from UT).
The other 19 cards are all Generated cards, coming from a wide selection of sources like monster effects (such as Snail Trainer's Thundersnail), Artifacts (such as Noodles' Instant Noodles), other spell cards (such as those from Blitz Quiz) and even a single case of a SOUL Passive, being Bravery's Recruitment (the only Generated card using a colored name).
Almost all monsters have an ability, each different from another. There are quite a few different methods of activating these abilities:
- Disarmed: Monsters with this ability can not attack during their turn, even if they have 1 or more ATK. They are still able to do that damage while defending.
- It's the only negative ability, and will be removed by Asriel.
- This used to be Can't attack.
- Charge: These monsters can attack right after being placed. Other monsters need to wait until the next turn in order to attack.
- Haste: This works the same as Charge, but monsters can't attack the enemy directly on the first turn.
- Taunt: Enemy monsters must target these kind of monsters. They can't attack any other monster or the player. Effects and abilities are unaffected by it.
- Dodge: These monsters will take no damage the amount of times shown on the card. The number will decrease by 1 whenever they would take damage, except when a 0 ATK monster attacks it (leaving the Dodge counter unmoved).
- This used to reset at the start of the owner's turn (before KR).
- In a maintenance during Beta 14.1, this was changed to reset at the start of both players' turn, but it was undocumented and was considered a bug.
- Beta 18.0 [Undocumented]: Start of the owner's turn.
- Beta 19.0 [Undocumented]: Start of both players' turn.
- Beta 20.0: Resets at the start of the owner's turn.
- Beta 36.1: Dodge doesn't reset at all.
- Armor: Whenever monsters with this effect are about to take DMG, that DMG will be reduced by 1. This entirely negates effects like that of Undyne.
- Transparency: Monsters with this effect are unable to be targeted by spells, effects and monsters. This effect lasts until the start of the owner's next turn.
- Taunt and Invulnerability (Frisk & Rouxls Kaard) don't work while the monster also has this effect. When this is removed, they will work again. Invulnerability can also be given using Alphys' Royal Kindness.
- Prior to Beta 41.1, this effect was instead removed when the monster with the effect attacked.
- Candy: Monsters with this effect restore 3 HP at the end of their turn.
- Ranged: Monsters with this effect will not take DMG from counter-attacks.
- Since Beta 47.0, this no longer exists.
- Thorns: This activates when the monster is attacked. This ability deals the amount of DMG shown on the card to the attacker.
- This ability won first prize in Statustest, one of the many Undercards contests where you make custom cards, etc.
- Since Beta 49.0, this no longer exists.
- Turbo: These effects activate the moment the card with the effect is drawn from your deck.
- This effect existed before the keyword, in the form of Mines.
- Magic: These activate the moment you place them from your hand. Summoned monsters from cards like Igloo and Lamp don't activate it.
- This used to be Battlecry, followed by Enter.
- Synergy: Exactly like Magic, but it will only trigger if you have also played a monster of the same Tribe as it beforehand on the same turn. (If the monster has both Magic and Synergy, the latter can affect the former if it triggers, depending on the card.)
- As such, this ability is unable to be used by Tribeless monsters.
- Delay: Another Magic-like effect, but this one will activate at the end of the turn it's triggered, making it function like a very short Future effect and a one-time unsilenceable Turn end effect.
- Future: These monsters have an ability that will activate after the number of turns shown on the card, like a delayed Magic effect. Silencing or even killing the monster won't stop the effect from activating.
- Since Beta 46.0, this no longer exists. Instead, we have Synergy.
- Support: This effect activates when an ally monster, except for the monster that has the effect itself, is about to attack, similar to when Blue Laser activates.
- Shock: This effect activates when you cast a spell (so not a spell casted due to another effect) with a base cost of 2G or more (so it still works if its cost was reduced to 0-1G).
- Turn start: As the name implies, these abilities activate at the start of every turn as long as the monster is alive and isn't Silenced.
- This used to be "At the start of your turn, ...".
- This was followed by Start of turn.
- Turn end: These abilities function similar to the previous one, but will obviously activate at the end of every turn. This includes the turn in which they have been placed.
- This used to be "At the end of your turn, ...".
- This was followed by End of turn.
- Dust: These activate once the monster that has it dies. Returning these monsters to the owner's hand or deck with cards like Doggo, Endogeny and Memory Head won't activate them. They also won't be activated if they die while being Silenced with the help of cards like Scarf Mouse or Nacarat Jester.
- This used to be Deathrattle, followed by Death.
- Others: There are also abilities that don't follow any of these rules, but have their own way of triggering. Abilities like these include 'Whenever this monster is damaged...' or 'Whenever a monster is summoned...'.
With all this in mind, some spells and monsters (and even the passive effect of some Souls) can inflict a Status Effect on other monsters, all of which are negative and thus removable by cards like Asriel, just like "Disarmed":
- Silence: If a monster gets Silenced, it loses all its abilities and will be reset to its base ATK and Max HP. However, if its Current HP is lower, it will not be restored to full health.
- Determination monsters are immune to this effect.
- Silence will also remove the following 2 status effects.
- Paralyze: When a monster is paralyzed, it is unable to attack on its next turn. But until it's unparalyzed, the monster is unable to be paralyzed again. (Removing the paralysis with effects like Silence or Heal and then paralyzing it again still works.)
- KR: Monsters with this effect will take 1 damage at the start of their turn.
- Dodge loses 1 counter instead, and Armor blocks it completely.
- Burn: An effect exclusive to the Boss Battle against Toriel. As such, this effect is currently unused. The Boss would give +1 Burn to all your monsters when its turn ended (+2 in Bad Time Mode). For each Burn a monster has, it would deal 1 DMG to its owner when their turn starts. Because it's inflicted when the Boss' turn ends and triggers when your turn starts, the damage it deals will be done right away.