Elves as PCs in most games tend to be super-humans with all the timeless grace and beauty of old Hollywood. They aren't really very different from humans, just prettier versions that are immune to ageing and charm. So what's the point? You can choose your character's age and appearance so the advantages of elfdom are few and not terribly interesting.
One of my favourite versions of "the world's most popular fantasy role-playing game" compounds this problem by placing its adventures in the early modern era of the real world. Lamentations of the Flame Princess has seven classes, one of which is the Elf. To play a human-only game would mean giving up nearly half of the payable classes. That means some reworking of what is there. Some of them are easy, the Dwarf class could be turned into a Barbarian just by replacing the Architecture skill with Climb and allowing them to be taller.
The Elf as a class is a lot more involved. It can fight well, cast magic, it has weird immunities and it's not quite in step with the world as it is. The best way to get all of these things and be human is voluntary demonic possession.
I like the idea of a Diabolist. A person who invites demons to share their bodies in exchange for power is pretty much the opposite of the idea of the elf while explaining all of the elfy class abilities.
The way it would work is the character knows a ritual for summoning creatures from a dimension that borders on ours. Creatures that can't physically manifest but can inhabit willing and unwilling hosts. While they ride the edge inside a host they can interact with the world in some special way that looks a lot like the spells of other classes. It is a dangerous trade-off for power. Also, sharing a body with extra-dimensional beings would have a few side effects.
These side effects would explain most of the class abilities and add some flavour. Some of these side effects are positive. With all the extra voices in their heads, Diabolists notice more than the average person so they get an enhanced Search score. As the Diabolist advances in level the voices multiply and the control of them improves so the Search skill improves as shown for the Elf class. This same hyper-awareness makes them difficult to sneak up on, resulting in a one-in-six chance to be surprised instead of the regular two-in-six chance. Charm and Sleep would also be ineffective against them because it would be impossible to target the host's mind amongst all those others in there. As a possessed creature and the host to extra-dimensional beings bent the destruction of our reality the Diabolist is of Chaotic Alignment, is detectable as such and can be turned by a Cleric.
These demons hate our reality and our world. The reasons are unintelligible to us as their goals are so alien. Exposure to that hate makes the Diabolist aggressive. This aggression makes them fierce combatants and allows them to use all the martial manoeuvres available to Fighters (Press and Defensive Fighting).
Elfs look different, with exaggerated features, strange eye colours and pointy ears. Diabolists tend to look different from the average human as well. If they're lucky, they'll have pointed ears. The presence of demons in a body is going to cause some pressure, especially as they manifest their power. Diabolists are in a constant fight for possession of their own bodies. This internal conflict leads to changes in the Diabolist's appearance. Part of the inspiration for this class was this image I first saw a few years ago. The obvious loss of humanity in exchange for power needs a mechanical expression for LotFP. Tying it into the acquisition of spells and the option to push things a little too far is the cherry on top for the Diabolist Class.
(Update: Thanks to Zach Marx Weber and Wayne Snyder who let me know this awesome image was created by Doug Kovacs for the Dungeon Crawl Classics core rulebook. I'm going to need to check that out! You can find more of Doug Kovacs' art here!)
For this I need a random chart. I don't have it yet, but I plan to put together a chart of mutations with three progressions for each roll of any single number. After three, repeated results mean two more rolls (which can just keep going if a player is particularly unlucky). An example of the three entries could be horns. The first time the horns would be relatively small and not difficult to hide. The second time they'd be grow to be larger and curl upward and possibly outward. Not impossible to hide, but certainly more difficult. The last result for horns would give the PC large horns like a big ram's that curl around the head and are virtually impossible to hide. Eyes could progress from strange colour, to glowing in darkness to glowing bright enough to show in the daytime. The farther down the line they get the more likely the PC will be burned as a witch. To get a good number and fit the situation I'd go with a D666 table. Using 3D6 with each die as a hundred, ten and single digit. So three ones (111) would be one-hundred-and-eleven. That gives 216 possibilities, which seems like plenty to me. Obviously three different colours would be useful, but a single D6 could just be rolled three times in a pinch.
The only problem is the spells. Sure they could just sacrifice some little creature every morning for each demonic presence (spell) to prepare a spell in the same way a Magic User memorizes a spell from their book. That falls short of what could be done with the class though. A Diabolist should be a different sort of caster. With their own method of learning spells, their own spell list and custom descriptions to turn up the weird on the class. Diabolists are bad people. They have sold their souls for power in the worst way. Diabolists still need to concentrate to harness the power of the demons inhabiting them though, so all the regular limitations of spellcasting apply. Except that it doesn't require the intricate movements that Magic User spells do, so a Diaboist can cast spells when heavily encumbered and with only one hand free.
A Diabolist starts with three randomly assigned spells/demons and a random mutation. For every level a Diabolist gains the PC can use a ritual to add a new spell/demon. They don't have to use it right away. They can wait until they are higher levels in hopes of attracting a better class of demon and having more high-level spells, since they can only summon a demon with an ability of a spell level that they can cast. When they cast the ritual they need to sacrifice an innocent creature. Any animal will do. It is painful and likely to be loud so the PC will need some privacy for the process that will last the whole night. The player chooses the spell level. Fifty silver pieces per spell level needs to be spent on materials for the ritual as well. At the end of the night the player rolls a save verses magic minus the level of the spell. If they fail they get a random mutation but they also get a randomly rolled spell of the level they chose no matter what the result of the save. If they roll a spell they already have, they get to pick one.
If a player is ruthless they can use a human sacrifice to automatically pick the spell they want or roll for two spells of a given level. The extra anguish provided by a person allows the PC to have more control of the ritual and its results. It also means an automatic roll on the mutations table. The Referee should make sure these kinds of murders are recognizable and cause more than a little uproar in a community when discovered. Players should also keep in mind that the weird guy with the glowing eyes is definitely going to be blamed when people start mysteriously disappearing so there are plenty of good reasons to avoid this option.
Casting spells is the other departure from the regular rules. Diabolists would use the spell progression table for the Elf to get a total for spell levels that can be cast safely in a day. A first-level Diabolist would only have one spell level, but a fourth-level Diabolist would have six (1x2 and 2x2)! Diabolists don't need to prepare their spells, they can't forget with those demons bouncing around in their heads, but coaxing their passengers into doing what they want takes concentration and gets difficult the more often they access any one demon's ability. The first time in a day the PC casts a spell is costs as many levels as it is. Each subsequent time it is cast in a 24-hour period or without at least six hours of sleep its cost goes up by one spell level.
For example, a fourth level Diabolist (let's call him or her Bob) has six spell levels per day. Bob casts Spider Climb (a level-one spell) and it uses up one of Bob's potential spell levels for the day, with five spell levels remaining. Bob casts it for a second time and it's harder, using two spell levels and only leaving three of Bob's total of six daily spell levels. That means Bob can cast Spider Climb one more time using all remaining spell levels without getting into trouble.
But what happens if the spell levels are just slightly over the daily allowance or the Diabolist wants to push their demons beyond the safe number castings in a day? That's where the 216 entries on the mutation table become important. If the caster has too few levels to cast a spell safely the PC can simply cast unsafely. They will receive a random mutation and must save verses Magic at a negative equal to the difference in levels or take 1D6 plus that difference in damage. Even if they fail the save the spell is cast successfully. For example, if Bob only has two spell levels left and wants to cast a spell worth four spell levels Bob needs to make a save against Magic at -2 or take 1D6+2 points of damage. If the caster has no spell levels left and wants to cast they take a random mutation and save against Magic or take the spell levels in D6s damage and the spell fails. So if Bob tries to cast a spell that costs three spell levels when he has no spell levels left it means risking 3D6 points of damage. A desperate move with no guarantee of success.
That's the basics of how I use the Elf class in my LotFP Early Modern Era Campaign. I'll add the spell list with custom descriptions later this week and maybe whip up the random mutation table too if there's enough interest.