Defense is a key concept to master in order to improve in Prismata. Defending properly will let you keep your attackers and production units alive longer and hopefully outlast your opponent. This page lists mechanics which can be taken advantage of to defend efficiently.
"In general, absorb is the strongest, most busted mechanic in the game, and you want to be taking advantage of it as often as possible." - Will Ma, Lunarch Studios Founder
Absorb refers to the ability of non-fragile units to take less than lethal damage and then instantly heal. It is a critically important concept to effective defense.
For example, Wall has 3. When defending, if the Wall takes 2 damage, the health will instantly return to 3 after the defense portion of the turn is completed and the two damage in question becomes absorbed with no effect. Compare to Aegis which has 5. If the Aegis takes 2 damage, it will not heal and will be left with 3 remaining and therefore the two damage in question has an effect. A defense based solely on fragile units loses the ability to take advantage of the absorb mechanic and is therefore not recommended.
When using a combination of fragile and non-fragile units in your defense, you want to use fragile units in a manner that maximizes your ability to absorb. Taking lethal damage with a fragile unit is acceptable if it allows you to absorb some of the remaining damage with a non-fragile unit. For example, with your opponent attacking for 7 damage you would want to defend with Aegis in front of Wall. The Aegis would take 5 damage, leaving 2 damage that could be absorbed on the Wall. By blocking in the other order, the Wall would die, leaving 4 damage to be taken by the Aegis. The Aegis would survive, but it would only have one health remaining compared to Wall's three health after healing.
In another example, if your opponent were attacking for 3 and you only had a Wall and an Aegis available for defense you are in a situation where you have no chance to absorb damage on this turn. However, defending with the Aegis and keeping the Wall alive will give the opportunity to use the remaining 2 health Aegis to maximize your absorb on a future turn (for example, if your opponent attacks for 4 on the next turn you can take 2 damage on the Aegis and then absorb 2 on the Wall). Clearly it is best to avoid these "no absorb" situations in the first place by having blockers with a variety of health values, but if you are forced into them (for example your opponent is using chill) remember to consider how to best maximize absorb on future turns if you have the option.
An exception to above rule would be when the fragile unit defender has an ability you wish to use, such as Protoplasm's ability to be sacrificed for . In Protoplasm's case you might even be able to maneuver your defense such that you can reduce Protoplam's health to 1 (putting it last and tanking 3 damage, potentially saving a defender like Wall) prior to activating the ability.
Defense that does not absorb but is simply sacrificed by assigning lethal damage to it is referred to as soak. While absorbers can be used in this capacity, they are usually not as efficient as non-absorbers (compare Energy Matrix with Aegis).
Defensive granularity is the term used for the ability of a defending player to block any given amount of damage by absorbing the maximum amount on his or her final blocker. A lack of granularity on defense will often lead to inefficient blocks and the need to sacrifice more defense than necessary. In addition, most optional attackers have an alternative benefit to opting for the attack. For instance, the Steelsplitter can block when it's does not attack, and the Militia can produce a gold. An attacking opponent can take advantage of a defense with poor granularity by attacking for less than his maximum potential and obtaining the alternative benefit on the attackers held back.
In some situations, it can be best to forgo the optimal absorb, to have more granular units in the next turns: Assigning the damage so the best absorb is possible (multiple times) later. See the first part of the Scrap and Scrutiny Expert Challenge for a playable example.
Example for the advantage of granularity while assigning damage to defensive units
If, for example, a player has only 2 Walls on defense, he will be forced to lose three defense whether he is attacked for 3, 4 or 5 damage. An opponent with 5 Militia can attack with 3 and click 2 of them for gold. If that player instead had 1 Wall and 3 Engineers on defense, he would be able to sacrifice only some of the engineers should his opponent attack for only 3 or 4 damage, rather than losing an entire three points of defense. Now, attacking for 3, 4, or 5 damage makes a difference since it changes the number of Engineers that are destroyed, so the opponent cannot obtain free gold.
Defending with non-Prompt units (preventive defense)
Prompt is a rather common feature for defensive units. However, non-Prompt defenders are often more cost-efficient than those with it (compare Infusion Grid with Wall and Perforator with Rhino), so it is often rewarding to plan ahead and buy non-Prompt defenders in advance.
Good fits for this strategy are units like Shredder or Perforator. Even if you have no intention to attack with them, their damage potential will count toward your attack total, complicating your opponent's defense. Cost-wise, even if you use them only for defense, Shredder provides an additional point of health compared to a Wall, and Perforator is 2 cheaper than Rhino. If you can manage to use the resource difference generated to buy constant damage, you will be outperforming an opponent defending solely with Prompt units.
- Prismata Game Analysis #6: Offensive Finesse, a video by Argeiphontes. (December 27th, 2014)