I have touched on heuristics previously, and all the concepts here have been brought up on Timeshapers in one way or another. However, I think it will be useful to aggregate those topics into a a single post that can be easily shared, particularly with new players.

I did not rank the Heuristics by importance, as the game is a bit too young at the time of writing to be certain about which is more important, or even if they are all true.

What are Heuristics?

A heuristic technique, or a heuristic, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, short-term goal or approximation.

wikipedia

Heuristics are more commonly known as rules of thumb. It’s a shortcut to doing a lot of computation. Given any decision, if there is a choice that is correct most of the time (think 80% or higher), and can be summarized succinctly, then that summary is a heuristic.

It is important to remember than any Heuristic we define is not guaranteed to be correct. But if you’re unsure, chances are it is correct. It is often said that good plyers follow Heuristics and great players know when to break it, so there is definitely a time to break them. But don’t break them often, because you will start to infringe on the territory where they are correct.

One of the most difficult things to do is test when breaking a Heuristic is correct. You often wouldn’t be able to see the effects of breaking (or following) a Heuristic until several turns later, and at that point in time, it would be hard to backtrack it to that decision point. But it is possible, if you make a mental note: “I have broken a Heuristic, let me see what happens now”.

Play Hand + Board

I have covered hand + board a few times before. One of the things I see players often doing is only counting hand instead of hand + board. This often results in something like:
Call house 1 – play 2 creatures and 2 actions.
Call house 2 – play 2 actions and 1 creature.
Call house 3 – play 3 creatures and 2 actions.
Opponent plays a board clear.
Then when you go back to call house 1 again, those creatures are gone and you never got to use them. Now I won’t say this never works, it certainly does, especially in good old CotA rush decks. Which I think is why players sometimes get stuck playing this way, because it does work. But the fact it works doesn’t mean there isn’t a better way.
If you cycle between house 1 and house 2, or even call the same house twice in a row to utilize the board, you’re going to get a lot more oomph out of your cards.

Generally speaking, there needs to be a very good reason to break this Heuristic, and I think that the majority of players would benefit from following it a little more closely. I will say that there is a fairly common counter Heuristic that I found.

If playing hand + board doesn’t use any hand cards AND (it does not get you to check OR your opponent’s delta is higher), it is probably an incorrect move.

This situation usually happens when you have a board of four or more creatures. Otherwise, barring hand size restrictions, you’d have at least 3 cards in hand of a house and 3 creatures on board, so the Hand + Board would be, at worst, the same for all houses. Reaping for 4 can be powerful, but it is less so if it doesn’t force your opponent to respond, or if your opponent can reap for 5 or more.

EDIT: There was some debate if this Heuristic still holds true with current sets, so I went back to the games I have played in The Big One 2, which was Archon Solo DT only. I counted the decisions I have made and these are the results:
I counted a total of 45 turns.
29 or 64.4% of which I went hand + board
8 or 17.8% of which there was an even choice and I went with one of them.
8 or 17.8% of which I did not go with hand + board.
I expect this Heuristic to hold true about 80% of the time.
When I deviated from the Heuristic it was for one of three reasons:

• Kill an important target or board clear.
• Make a big play.
• Grow the number of cards of a specific house in my hand in preparation for a big play.

Considering an average game is about 10 turns, you should expect to deviate from this Heuristic about twice a game.

Don’t hold cards

Players coming from other games, or even brand new card game players will often see a very powerful effect and hold onto it for long periods of time. One of the first level-ups a player can achieve in their gameplay is to not hold those powerful, situational effects.

Gateway to Dis is a very powerful card, but if your opponent doesn’t have a significant board advantage then it is not worth playing, and therefore likely not worth holding.

However, like every Heuristic, there are times to break it. If you know your opponent has the potential to generate a big board it might be worthwhile keeping a Gateway for a rainy day, but the question must be what is it going to cost you. Holding cards has been equated to chaining yourself, which I have shown to be untrue, provided you actually use the card the next time you call the house again. This means you need to be fairly certain the card is going to be used the next time you call that house, or you are doing yourself an injustice.

Reduce your opponent’s delta to 2

In KeyForge, Reaping is better than fighting, but I find that to be an oversimplified Heuristic that isn’t sufficiently practical. Reducing your opponent’s delta to 2, however, is much more practical. If you have ready creatures and are considering which to use to fight and which to reap, a good rule of thumb is that you’d want your opponent’s delta to be no higher than 2.

Generally speaking, if your opponent is reaping for 2, which is a third of a key, you’re probably going to be fine. While if they reap for 3 or more, it might start being debilitating. While this is a very good Heuristic, like all other Heuristics, there are times to break it. But this one here is a much harder to define a counter-heuristic for. Breaking this Heuristic would need to take into account the key situation, the aember situation, the style of deck you’re playing and often how sure you are of which house your opponent is going to call next. Still, if you follow this Heuristic, especially in sealed games, you’re going to do well more often than not.

Kill the Witch

One Heuristic that complements the previous one is killing the Witch. And by Witch I don’t mean any woman that seems a little too smart for her own good, so she must be burned at the stake. Likewise I don’t mean just any creature with the witch type. When KeyForge players say to kill the witch, what they mean is to kill any creature that can, on it’s own, produce a significant advantage to your opponent.

This Heuristic can be used in conjunction with the previous Heuristic. You could translate a Witch’s ability into a delta, and then decide if it must die. For Example, the original Witch:

Witch of the Eye has a delta of at least 2 on her own, since on a reap she will not only get the aember from the reap, but also to replay a card, probably worth at least one aember. You could look over your opponent’s discard pile and see which actions are available to them, and what kind of value they provide. Suffice it to say that unless it is very early and their discard pile is empty, WotE has a delta of more than 2 on her own, which according to the previous Heuristic: She. Must. Die.

ABC – Always be checking

Due to the very nature of keyforge, going to check means your opponent is forced to respond. Forcing your opponent to do something is good. You don’t need to look further than Control the Weak to know that.

Control the Weak can force your opponent into a house that provides suboptimal plays, and so can going to check. If your opponent has aember control only in one house in hand, they might be forced to call that house in order to stop you. You have essentially created a Control the Weak by going to check.

Though I said I won’t rank them, this is likely the top Heuristic in Keyforge. If you can get to check it is almost universally better than not doing so. A common exception might be that your opponent is about to forge themselves, in which case the Heuristic still stand, but your opponent got the jump on you. Otherwise not going to check would probably mean you are following one of the other four Heuristic.