As this is my first post here - hello everyone!
Before I start - I am not native English speaker, but I am trying my best to write without making big errors (I had English back in school times and didn’t had any problems with it, but feel that I am mostly self-taught anyway). If you see any - write about that, so I will avoid making the same mistakes in a future! 
I have idea for a RPG-like game with strong, but not completely dominant transformation elements - mainly weight gain, shrinking/growing, various mutations (as long as character is still mostly human-like, other races is a big “no”).
It is in sci-fi setting, but don’t expect lots of scientific correctness other than enough to keep it non-absurd - this is game with transformation elements after all, and while I want to find balance between sci-fi and fantasy, I don’t want science to limit the possibilities.
This idea ?sprouts? in my head since a few days, and I think it is finally thought and polished enough to present it. Be warned - HUGE wall of text coming.
Backstory
In 2170, scientists find a weird anomaly in the Jovian gravity field. They send unmanned probes to find out what is happening, but contact with all of them is lost just before being close enough to where they would be able to take precise measurements. Finally, in 2174 contact with one of the probes was recovered. Most of its systems malfunctioned because of very strong electromagnetic impulse, but some of the modules including low-resolution camera, atmosphere survey module and relay survived. It transferred the data back to Earth, where scientists went speechless…
Earth… Or not, look at these landmasses - they are very different from Earth ones! Further photographs revealed that this planet have not one large moon, but two smaller ones, so this is for sure a different planet. Atmosphere survey made using small capsule dropped into the atmosphere revealed that it have atmosphere comparable to Earth - with slightly less oxygen and different trace gases, but still highly habitable by humans. Capsule also captured a few pictures of the surface revealing alien foliage, but sadly it didn’t survived the impact as parachute was suited for a much denser, Jovian clouds.
Remaining data shown that the probe survived transition from Jupiter to unknown planet in perfect condition, but travel back destroyed most of its systems. Despite of that, this discovery was too important to discard it. Decision was made to send two manned ships into the anomaly, in a potentially suicidal mission. The plan was to send first 100 people by the first 10 years, and then start sending more and more humans every 10 years. The whole mission remained secret.
Both of the first ships were designed to the equal amount of men and woman, both with 50 crew members. As space ships at this time have very reliable autopilot systems already and no human can even get close to them, the whole crew was randomly chosen from the citizens of USA (they are funding this mission, so they obviously want to gain something from it), with enough genetic, looks, talent and character diversity to increase chances of survival. All of them were before their 20’, but at the time of arrival they will be in their early and mid twenties. To keep the mission secret, government made sure that they will “mysteriously” disappear (how - this is different matter).
Story start and character creation
For people who tl’dr the backstory - anomaly on Jupiter was discovered, probes sent to research it, Earth-like planet found on the other side of anomaly, potentially suicidal manned mission sent to it with 50 young man and 50 young woman in two different ships.
We are one of the woman (one gender only planned so far, because this means MUCH less writing - and I want to focus more on mechanics than having to create two/three different variations of many situations requiring more excessive descriptions) abroad the second ship which is meant to enter the anomaly few months after the first one. This is the time when we can create our character.
Character creation is split into few different sections: at first, we have physical characteristics. Some of them are “free” to change as they don’t influence the gameplay difficulty too much (for example, body shape), but others, like height, muscle mass, stomach capacity or “tools” size (paradoxically smaller can make some encounters I have in mind easier) require points to be spent or freed in order to change. We can assume that only physically fit people were chosen, so no weight changing at start.
Second character creation section is choosing your past - it influences your initial statistics. In a future education takes much shorter time due to research on direct brain stimulation, so most of possible options will be related to previous job. There will be choices that make the initial stages of the game easier, as well as the ones that make it harder.
Third and last stage is distributing points between resistances: these will be gained very slowly during the gameplay, so this choice is relatively important. These resistances are:
[ul][li]Weight penalty resistance (how much additional weight is slowing your character down and when the penalty starts)[/li]
[li]Lust resistance (obvious)[/li]
[li]Mutation resistance (vulnerability to mutations while staying outside of ship rises slower, mutation meter due to encounters rise slower - many players will obviously want to keep this resistance low, but to balance things it will also rapidly jump up with every mutation gained)[/li]
[li]Poison resistance (obvious - there are many different poisons and most enemies use them)[/li]
[li]Pain resistance (you can give in to pain or be affected by it negatively)[/li]
[li]Suggestion resistance (similar to lust resistance, but more related to hypnosis and similar situations)[/li][/ul]
After creating a character, you are presented with situation after reaching the anomaly - your ship enters it, anomaly violently closes behind it damaging the engines, so the ship is forced to make an emergency landing on the planet. The landing is very rough and many people don?t survive it, but the ship managed to crash very close to the first ship. What you see at location is frightening - while people from first ship are still humans, something changed them. Almost all of them show different signs of mutations, it also seems that not all of them made it as well. On the good side, they discovered that someone was there before, but is a long gone (probably?) - and left some schematics that are useful, including very important one - the body link machine. Its concept is very similar to cloning machine, but it operates differently - it ?links? to one person, creating the exact replica in the inside chamber. It is the mirror copy of the person outside it, affected by all permanent changes to body and mind of the user. Machines are not working perfectly, so in case of death minor amount of knowledge is lost. What else is lost is a matter of further thinking, I am on the edge especially with more short-term changes (like too much liquids and/or gasses in organism) and parasites.
Skills
I touched topic of statistics a bit earlier, I think this is time to explain it a little bit.
All statistics are raised as you use it. For example, you can become better melee weapon user when using melee weapons, or dodge attacks better when dodging. The same principle with resistances, but they rise much slower than statistics.
At this stage I obviously don?t know how much statistics will be needed exactly, but examples of the obvious ones include:
[ul][li]Melee weapons[/li]
[li]Ranged weapons[/li]
[li]Dodging[/li]
[li]Blocking[/li]
[li]Athletics[/li]
[li]Hacking[/li]
[li]Perception[/li][/ul]
World navigation
World shape is always the same every time you replay the game - that is, all major passages and places will be always in the same places. Initially the whole navigation will be based on simply having the list of locations where you can go. Map is a possibility later on, but I am terrible at doing any art, so don?t really hope it will appear even later on (maybe except the very simple one).
All places on map can be divided into three major categories:
[ul][li]One-time encounters[/li]
[li]Repeatable encounters (think: something like Tainted Elysium ones)[/li]
[li]Dungeon-like areas[/li][/ul]
Dungeon-like areas are the most interesting: if you ever played any roguelike game, this is exactly what I have in mind.
Combat
Combat in my idea is tick-based: for example, let?s assume that your character does every action at constant 300 ticks, while your enemy does them at 200 ticks and you both start at zero ticks. For example:
Tick 0: both you and enemy do nothing
Tick 200: enemy does action
Tick 300: you do action
Tick 400: enemy does action
Tick 600: you do action (in case of equal tick time, player is always first)
Tick 600: enemy does action
Tick 800: enemy does action
Obviously, this means that different actions can have different tick times and skills/equipment can also influence that.
Ticks are used not only for combat - most actions outside of it will have ticks as well.
But how the combat exactly looks like? It will always happen on something like one-dimensional line, where you are on the left and enemy/enemies are on the right. Distance between you can change, so for example as a melee character you will most likely want to close the distance fast. Like I mentioned earlier in this section, actions have different tick times, and there are ones you do consciously as well as the automatic ones (like dodging, blocking, reaction to pain).
Vitals
Vitals include:
Health
This one is more complex than just simple ?HP?. Your character can have wounds stacked on her, and every wound reduces the global life pool. Once you hit 0 you obviously die, but pain related to low HP can have effects earlier. Wounds are here for two reasons - first of all, there can be different ways to heal them. Some of them turn into other kinds of wounds over time, some become smaller over time, some are getting worse. Second, this is a good way to include ?effect over time? you might want to get rid of or ignore for? Various effects, which you will see a bit later.
Stamina
Stamina can be used for multiple things - it can be used in various encounters, as well as in combat. If you know how stamina works in most games, you are in home.
Radioactivity
This is the interesting one. Initially you have zero radioactivity, but every mutation on you increase your limits. It works similar to stamina, except much slower regeneration and usage concentrated around abilities gained with mutations.
Lust
Pretty obvious one, shamelessly borrowed from Tainted Elysium (which is one of main inspirations for this idea).
Insanity
Similar to lust in effects, except that it is related to mind-twisting situations rather than the sexual ones.
Monsters
There are some very early concepts of possible monsters that could appear in game. They don?t even have any names, this is simply a concept. I do not include any ?classical? RPG monsters here, but they could appear (with more or less twists).
Spider-like small creature
This creature is small compared to your character (something like 30-40 cm sounds right). In combat, it tries to stay away from you, is very good at avoiding stuff and shoots hard to avoid poisoned stings. These stings don?t hurt you too much, but there is one twist - the poison in them makes you temporarily shrink (with body mass ratio staying constant somehow and your armor shrinking together with you, but weapons staying the same size - that is, after some time you can be simply too small to wield them… And let’s just forget about the ones in inventory 
). When you are small enough, spider closes distance and eats you with its jaw.
In addition to poison being? Poisonous, it raises your mutation meter for this exact creature (every creature/encounter type having different mutation meter and mutations possible). If you spend more time outside of ship, it rises even quicker, and once it gets to 100% you can?t do anything to prevent mutation.
Mutations from this creature could include (keep in mind - the whole creatures part is very early concept and it requires lots of thinking to keep it interesting and balanced, so take this with a grain of salt - and I am including mutations only for this spider so far) ability to shoot stings with shrinking poison yourself, spider-like eyes making your perception in a dark better at the cost of light perception or spider-like jaw (poisoned as well, of course… And yes, with possible use not only in combat).
Incubus-like creature
Fighting with it will obviously cause your lust meter to rise quickly. When it reaches max without you defeating this creature, you literally become subjected to it? To the what degree - this is something I would like to skip for now, but it usually ends pretty bad or very bad for your character? Unless you have one of its mutations. Its combat style initially tries to hurt/weaken you while also increasing your lust, but once you are weak enough it tries to increase your lust only.
Puff mushroom
Sentient, partially mushroom-like and humanoid-like creature, able to cover the battleground with gas which quickly gets inside your character body, temporarily swelling it. Open wounds cause the gas to fill you quickier. Other than that, combat with it is pretty straightforward - it obviously want to hurt you in order for you to either die due to wounds or explosion from the inside.
Fake treasure chest
Opening most treasure chests require taking part in hacking minigame (or making attempt to resolve it automatically if you don?t like it). Fake treasure chests add a little twist to it - there is obviously no treasure inside, but you must complete the minigame anyway. While you are doing that, your insanity meter rises and if it reaches 100% you fall inside the ?chest?, where it causes damage to you as well as infecting you with a brain parasite forcing you to try to open any encountered chest. If you complete the minigame successfully before the time runs out, encounter changes into the normal combat always starting at the point blank range (but the chest is obviously not very mobile).
Summary
When it comes to development side - if this idea receives enough feedback to make me feel like someone would actually want to play it (I am very feedback-driven), I will most likely start developing it. When it comes to platform, as I don?t plan any graphical fireworks and I have many years of experience in it already my platform of choice would be probably Java desktop application (GUI framework: JavaFX), although I know a fair bit of Unity, HTML5 and Haxe as well. Graphics are much more difficult subject, like I mentioned once in this post I am terrible at doing any sort of graphics, so the game would most likely be mostly text-based (with some very simple graphics/animations for combat module and later on a global map module)… Unless I will find a capable artist of course, but this is very unlikely.
If anyone survived to this point (I hope someone actually read all of that )… What do you think about that? This is obviously not completely finished concept (things like example areas, equipment, hacking minigame missing completely), but I think it already shows enough points to go somewhere with it (this forum) and ask for opinions. Would you like to play something like that? What would you suggest to make things even more interesting?