Among the games I have been playing during my break from blogging is Romancing SaGa, a somewhat older game for the PS2 I recently stumbled across. While Romancing SaGa is a remake of an old SNES RPG that never made it state-side, it is pretty clear that it is a loose remake, since there are some pretty interesting innovations derived from more recent SaGa games. One of the best of these innovations is the BP/DP system, which is involved in the costs for using the various spells and special weapon techniques in the game. This system is light-years ahead of traditional MP costs and results in much more dynamic and strategic combat.
BP is short for "Battle Points", and it is the primarily limiting factor on what special moves that you can use in battle. Unlike in a traditional MP system, where characters have MP totals that are carried over between battles, BP resets at the beginning of every encounter. Each character has three pertinent BP values: their starting BP amount, their maximum BP total, and the amount of BP that they gain at the start of each turn of combat. As such, a character's BP total is in constant flux, going up and down as the battle progresses and the character uses his spells and special moves, which in turn means that what moves the player has access to are also in constant flux. For example, a character who starts a fight may have to wait until turn 2 before he can cast a certain spell. However, if that character keeps using weaker spells in the mean-time, he might never get to use the stronger spell. So, BP makes the player have to constantly weigh the opportunity cost of actions.
I find that this approach is much more interesting than the traditional per-adventure MP model, which doesn't usually force the player to make interesting resource-management decisions on a round-to-round basis. In most RPGs that use MP, the dominant strategy consists of two parts: conserve MP as much as possible during regular battles, then use your MP with complete abandon during boss battles. Even if MP gets low, there are typically plenty of items available to restore it, so low MP is rarely a factor in determining which move a character has access to in a major battle. In the BP system though, the best special moves often consume from a quarter to half of a character's max total. So even though it is constantly regenerating, using your best attacks constantly isn't necessarily a good idea. On the other hand, since BP is encounter based, it means that characters can use their various special moves without worrying about saving them for boss battles, which makes regular battles generally more exciting.
However, the biggest innovation of Romancing SaGa is that it does incorporate aspects of more traditional per-adventure resource management as well using DP (Durability Points). DP isn't a character statistic; rather, it is a quality of equipped weapons. A weapon has a maximum DP ranging from 20 to 60 or so, with 50 being pretty common. Attacks can deplete anywhere from 0 to 10 DP with each use, and when a weapon reaches 0 DP, it becomes useless until repaired. However, normal weapons can only have their DP restored by resting in an inn, while special weapons can only be repaired by forking over a lot of money to a blacksmith. As such, it is usually worth conserving DP until you need it. However, an interesting effect of the DP system is that it encourages characters to carry multiple weapons (such as a regular weapon to use DP draining attacks with and a more expensive weapon to use low DP attacks with), which adds some interesting tactical layers to combat.
Where the BP and DP systems really shine is in how they interact. Since every attack has two costs, the system allows for a wide range of special moves that are useful in an equally wide range of uses. For example, weak, low BP, zero DP cost attacks are great for saving up BP for a bigger attack when dealing with normal enemies. High damage, high BP, low DP attacks are good at quickly eliminating regular enemies, but are generally unsustainable during protracted combat. High damage, low BP, high DP attacks are great for dealing solid damage to a boss round after round, but they chew through weapons and are thus useless for fighting regular enemies. Since exact details such as individual BP regeneration rates, current BP totals, what weapons are available, what the costs of various moves are, and so forth are so variable, there are rarely obvious choices to make. The sum result is that each character has a wide range of interesting moves available and the player is forced to make interesting resource management decisions every turn.
However, the system does have a few weakpoints. Most notably, spells use BP, but not DP; instead, powerful spells consume a character's LP (Life Points). However, each character only has six to eight or so LP, and when they run out, they die. Since this is hardly the only way to lose LP in a fight either, using spells with an LP cost can be suicidal. Another problem is that the number of actually usable moves is a lot lower than it could of been due to poor balancing of moves and limited availability of various special moves. The system could definitely use some tweaking and refinement.
In the end though, I think that an RPG combat system that incorporates multiple resources instead of just one ultimately produces a more interesting combat experience than one that uses just one if handled well. Mixing per-encounter and per-adventure resources together works particularly well. I would definitely like to see more games use systems like this.