Combination Cards are cards that simply have effects based on what other cards have been played. They're a little difficult to explain, so an examples list would do better:
- The most common format of these is probably "If X is in play, Y's effect can be used", where X is a certain card or one of a set of similar or related cards, and Y can be anything, but is usually a point value. X is often generalised (e.g. "Any card with a triangle"). There is sometimes a point value regardless of whether X is in play, so the card isn't totally useless if you don't have X.
- The opposite to the above is also quite common. "Y, unless X is in play".
- Combinations of the two are also common. "If X is in play, you can do Y. If A is in play, you can do B. But if C is in play, you don't do anything, regardless of whether X or A is on the table."
- Cards based around "find the other half/quarters of the picture on this card" are also quite common.
- There also exist cards designed to match any half picture, usually rendering the effect of the card with the picture void.
- These get really fun when a card forms half/quarters of more than one picture at the same time. In my deck, there are many cards with quarters of geometric shapes in each corner, and if you finish one of the shapes with other such cards, you get to take either of the point values(Each quarter of the shapes has half of a number on it, leading to two numbers when all four are matched up).
- More exotic forms also appear once in a while.
- Pieces of a fairly large map, with a huge reward of completing the map, sometimes appear.
- Pieces of a snakes and ladders board.
- Objects in a fairly large and recognizable sequence, such as letters of the alphabet or consecutive numbers.