Unpredictability and Control in Turn-based Combat

Sinister Design's Craig Stern has penned an interesting piece that dives into "an examination" of the "unpredictability and control" of turn-based combat. Uncertain outcomes, tactical complexity, and the role that randomization plays are all discussed at length:
The most conspicuous of my concessions to randomized results lies in the use of negative status effects. Negative status effects are a common feature in turn-based combat systems. They lend depth to RPG combat by creating secondary objectives (e.g. cure poison as soon as possible to minimize damage) or by changing the resources at various player's disposal (e.g. muted characters cannot use magic until cured).

Despite their utility, negative status effects have been almost entirely absent from Telepath titles up until now. (Craig,) you ask, (why would you create a strategy RPG that excludes such a useful and obvious tool for increasing tactical depth?) The reason, quite simply, is that previous Telepath games employed a combat system that was almost 100% deterministic. Most negative status effects, in turn, are simply too powerful to use in such a deterministic environment!

Consider an attack that imparts (Frozen) status, for instance. If this status effect hit 100% of the time, Cryokineticists and Frost Spriggats would become game-breakingly powerful. Imagine going up against an opponent with an army composed entirely of characters that freeze your units solid for 2-3 turns on their first attack; there would be almost no way to successfully engage them. This same problem applies to Sleep, Stun, or any sort of common RPG status effect which prevents a character from acting.

Even a milder status effect, like (blind,) would become overpowered in a deterministic system. Not only it would take effect 100% of the time, it would necessarily cause the hit rate on physical attacks to drop all the way to 0%! Blind would essentially become an automatic Render Physical Attacker Completely Useless card.

The solution I chose was to make negative status effects take hold only some of the time. This limited application of randomized results turns negative status effects from a way of automatically crippling the enemy into a gambit you can try and for which you had best have a contingency plan in case of failure!

...

In a spatial turn-based combat system, unpredictable enemy unit composition and positioning under a fog of war mimics much of the effect of a randomized hand of cards. The player must scout, or else take the risk inherent to issuing orders with incomplete information about what enemy characters the opponent has at its disposal. Other elements of the battlefield can be randomized as well: loot drops, spaces with healing or defense bonuses, and environmental hazards, to name a few.

Crucially, these each add unpredictability to the scenarios the player faces, and not to the results of individual player commands. The player is never compromised in his ability to control his characters; any random chance the player confronts in this way, the player has the opportunity to respond to and circumvent.

There is one other, major way that randomization can be used to foster unpredictability. You may recall me mentioning earlier the dangers of relying exclusively on clever AI to provide unpredictability in a game. No matter how clever an AI's programming, if its decision-making process is consistent from game to game, sooner or later the player is going to figure out how it thinks and learn to outwit it over and over again. The opponent will become predictable, in other words, and the game's tension will plummet.

This is a great place to employ randomization: add a random modifier to some of the AI's heuristics that change its priorities from battle to battle, or even from turn to turn. Also good: add a random coefficient to the scores the AI assigns to attack targets: small enough that the AI won't make ridiculous decisions, but big enough that its target priorities will be difficult to predict from attack to attack.