Shalev's Rule and Optionality

The Prismata development Team adopted a principle known as "Shalev's Rule." It states that anything players expect to be good should never be bad. For example, players expect having more units to be better in combat games. Mind-control as a mechanic breaks this expectation. You may think twice about summoning that Megadragon if you know your opponent can steal it from you!Prismata devs formalized a list of "Shalev's Domination Rules," abbreviated as SDR. They state which positions should always "dominate" others. However, Shalev's rule is useful even if you don't define SDR for your game. It is all about player expectations: players can set goals more easily when they have universal objectives. Personal progression is a great example of a natural SDR target. Players expect that anything framed as a progression reward will make them stronger. Upgrades with drawbacks can be jarring because they violate the implicit SDR target.You can often fix violations of Shalev's rule through optionality. The Prismata team originally had a "Plaguebearer" unit that dealt damage upon death. This created a situation where killing an enemy unit could be bad because it could harm the attacker. They fixed this by adding an option to trigger the effect manually:

To keep the unit SDR-compliant, we gave it the ability to self-sacrifice (hence killing it is never a bad thing, since your opponent can suicide it anyway!)

Another example comes from Rift Wizard 2. Players advance by learning new spells and unlocking buffs that improve the attributes of spells. One such attribute is duration: how long a spell lasts. Some spells like Searing Seal trigger an effect after their duration has elapsed. This means a longer duration can be bad if you need the effect sooner. A player expecting their duration buff to pay off could be unpleasantly surprised when it delays the effect they need. Rift Wizard 2 solves this by allowing the player to trigger the effect early when they recast the spell.In real life, options are universally valuable when holding them carries no risk. The same applies to games. If you have a cool mechanic that violates Shalev's Rule, you can often fix it by injecting optionality somewhere.

http://blog.prismata.net/2015/10/21/shalevs-rule-in-prismata/