I've been kind of thinking of an idea I'm tentatively calling the 'Combat Role System'. This establishes different roles within combat that might be served and applying xp multipliers based on those. I don't know if this is specifically what you're interested in, but I'll explain it anyway - maybe it will spark some other ideas. Essentially, the thinking is that xp has 2 components: Distance and Role.
Begin with your current distance-based xp system and cut those rates to a very low minimum. IMO, everyone on a battlefield that is somewhat close to a battle gets some measure of experience (based on the premise that being exposed to combat makes you more aware of combat tactics, which makes you more experienced). This base number is what possibly gets leeched.
Then, you add xp multipliers for different 'roles' or combat tiers that the PCs may play during the battle. In this way, you incent behaviors you want to see. These tiers are hierarchial and once a PC earns a tier in combat, they can't get bumped down to a lower tier for that creature. And, they only are assigned 1 Role during the combat for that creature (whichever is the highest role they achieved).
Each combat role has a different multiplier. What's more, this multiplier is based off a different xp base from the distance-based xp system.
Combat Roles could include:
- Killer (3x multiplier)
- Damager (2x multiplier)
- Combat Medic (2x multiplier)
- Buffer (1.2 multiplier)
- Participant (default - no multiplier)
- Non Participant (outside of distance area or exceeds level-gap - no xp)
For example:
Fighter, thief, mage, cleric of equal level meet a band of 7 orcs:
Fighter rushes in to attack, thief goes to flank, mage begins to cast fireball, and cleric casts bless.
Before the cleric finishes his spell, Fighter kills the first orc in 1 slash, earning him the 'Killer' role for that creature. The base distance xp system earns him 3xp, which is the same that everyone in the distance radius recieves. However, since he was the Killer, he gets to dip into the Combat Role System, which evaluates the CR of the orc and says that the base xp for that creature is 5 * his role multiplier. As Killer, his muliplier is 3, so he earns 15 for the kill, plus 3 for the distance-based xp = 18 total for the kill. All other party members recieve 3 for the kill.
Before the next orc drops, the cleric finishes his blessing, thus earning himself Combat Role System xp as well for the remainder of the combat, at least within the 'Buffer' tier (for creatures of this low CR, it only means an additional +1 xp point, though).
Mage's fireball immolates 4 of the remaining orcs (and severely damaging the thief). So he earns 72xp for the kills (4orcs x 18xp), while the other PCs earn 12 (4x3) each (the cleric earns an additional +4xp per his 'Buffer' role). Further, the mage has damaged the remaining 2 orcs, earning him a 'Damager' role on those two. If he manages to get some magic missles off and kill them before any others, he'll be promoted to Killer for any he actually kills, but he can't ever go lower than 'Damager' for those 2.
The thief, smoking greatlly and brows afire, eviserates one of the orcs from behind. He's now the Killer, earning 18xp while the others earn 3. Additionally, the mage, as the 'Damager' earns a multiplier of 2, earning him +10xp (13 total). And, the cleric earns +1xp as the 'Buffer' (4 total).
Nex, the cleric rushes in and casts CMW onto the thief, healing him. He has now been promoted from 'Buffer' to "Healer' in the combat, increasing his multiplier for the remaing orc.
When the fighter finally dispatches it, the fighter earns 18 (Killer), the mage earns 13 (Damager), the cleric earns 13 (Healer), and the thief earns 3 (Participant).
Total xp earned in the encounter is:
Fighter: 51
Thief: 46
Mage: 101
Cleric: 36
Technically, it might look like this:
- When damaged, a local int is written to the creature using a unique ID for the damaging PC. This is the 'Damager' tier.
- When a PC is healed while in combat (and the PC actually needs healing), a local is written to nearby creatures. This is the 'Combat Medic' tier.
- When a buff spell is cast while in combat, a local is written to nearby creatures. this is the 'Buffer' tier.
- OnDeath, the killer is the 'Killer' tier.
OnDeath, the distance-based xp system fires, granting small xp to each PC. It also checks that creature for a local equal to the unique idenfier for the PC. if found, the value of the local is the tier and the Combat Role xp system fires, granting additional xp to the PC based on a secondary CR table and the Role multiplier.