When I go to Dairy Queen and get an ice cream cone, I like to either get a vanilla/chocolate swirl or a vanilla cone dipped in chocolate. Sure I like either flavor alone, they stand up on their own very well. But there is something about that mix of flavors that offers a unique experience.
Yes yes, I'm getting to something RPG relevant, I promise! Ohhhh, the chocolate sprinkles! Labyrinth Lord and Mutant Future are a lot like that. I see LL as the vanilla, and MF as the chocolate. Alone they rock pretty hard, but mixed together and suddenly you have AC/DC meets Queen, and you better look out.
One of the challenges of such a delightfully unholy union is achieving something resembling balance. I addressed this in the Mutants & Mazes section of Mutant Future, and I think it worked out pretty well. The thing about "balance" in relation to these games is that it is a subjective thing. There is no hard and fast formula for it, like there are with other games that use for example a point buy system, or something like that.
The philosophy I used when approaching the M&M section was that mutant players in an LL game need to be able to have powers that increase with increased levels. In a straight up MF game, players start out powerful, so many components of a character are not as relevent to level advancement. So to achieve this incremental progress the powers had to be treated in many ways like spells for spell casting characters. Mutants become a class unto themselves, with the defining element being that they are mutants, just like the defining element for spell casters is that they can cast spells.
The result is something that I think works very well. A mutant can rub elbows with a thief, a cleric, a magic user, and still fight pretty effectively and whip out some mutational effect every so often (depending on the effect, every round, or twice a day, one a week, etc.). But....what if you want to be a mutant human thief, or a black-hearted simulacrum sorcerer?
Then the approach is going to have to be different. The mutant powers, for the sake of "balance," must be greatly reduced. Being a mutant or a biological android shifts to be a little more cosmetic. First, I suggest casting aside the idea that every race should be designed as its own class. If you want to create a variety of mutant/android races to use in your game, this is not only going to make it tedious from the design perspective but you will inevitably introduce a mess of different experience progression charts etc. In the end, it is cleaner and more efficient to treat the mutants as humans by separating race and class.
Whoa, hold on! Separate race and class in Labyrinth Lord. Sure! The tools are already there. If you want some help, I wrote a very straight-forward article on how to do this that can be found here.
Don't get me wrong, you certainly could design an awesome simulacrum sorcerer using the Elf class as a guide, with it's own unique spell progression and a few mutant powers. It would be cool. There is a place for those sorts of classes too. But I also think offering a flexible set of mutant "races" that can choose any class or a few restricted classes is an easy, great way to add diversity without having to wrestle with whether XP is balanced for each race.
Ok, so how to do this? First, use what you already have as an example. Look at the sorts of special abilities the demi-humans have, and shoot for a similar thing with a mutant race. Let's create one together.
I love the idea of a vat-born character becoming a sinister weaver of magic, so lets create one version of a biological android that can be a magic-user among other things. Here is one possibilitity:
Simulacrum variant race
Requirements: INT 9, DEX 9
Ability Modifiers: INT +1, CON -1
Prime Requisite: As class chosen
Classes Available/Level Limit: Fighter/5, Thief/7, Magic-User/10
The khorlans were designed to be the intellectual slaves of the Elder Race. Their initial purpose was to serve as scientists to develop ever increasingly destructive weapons for the Armageddon that eventual ripped the world apart. Khorlans are unable to reproduce on their own, and their communities are often centered around the remains of highly guarded functioning vat-machines, so that new arrivals may be brought into the community and educated. The ability to work with abstract scientific formulas has transferred easily to the concepts involved in working magic. Khorlans may be fighters, thieves, and magic-users. They were designed to look different from humans, and completely lack all pigment, having white hair, pearly white skin, and black eyes with no visible iris (i.e. bizarre appearance). In addition, they have the mutation neural telepathy, which was used to communicate with their highly mutated and alien masters. Khorlans receive the following saving throw bonuses, +1 versus spells, and +2 versus energy attacks.
Now of course I whipped this together fairly quickly and it hasn't been playtested, but this is just one example of how races might be created when combining LL and MF. When doing it this way, characters will advance in levels, to-hit, and saving throws exactly as the class chosen.