Just as it sounds, I'm in the process of designing a Mass Effect x MLP Crossover, and the specific setting I am working on leaves all kinds of room for other sources to be used in the crossover [provided they aren't utterly ridiculous... Gurren Lagaan would never fit for example]

I'm already working on the OC information, but I'll sum up the scheme of things for this interest check.

The Simple Theme: Over a thousand years after Shepard used the Crucible to Eliminate the Reaper threat, and indeed all known Synthetic life present in the galaxy at that time, The Galactic Civilization is well on it's way to being rebuilt, though the galactic isolation that persisted for centuries afterward gave rise to many a micro civilization born of time and lacking contact with the rest, until new relays are brought into use that ultimately reconnect the entire galaxy.

More importantly though, with the Reaper's failure to eliminate the civilization of the previous Cycle, It is inevitable that newly developing Races will encounter the old, some may clash, some might work well with them, others may simply wish to be left to their own devices in some lone corner of the galaxy they laid claim to during isolation. There is vast potential for things to develop down any number of paths.

Some may hate me for this, but yes, This particular iteration focuses on 'Equestria' being one of these advancing civilizations reaching the stars during the thousand years prior to Galactic reconnection, that includes any number of Species that exist on Equestria being playable in the RP [within reason, for instance, there's not much room for a full sized dragon, but then again, there's plenty of ways to get around that size issue. a Draconequus wouldn't make much sense either, as fun as the chaotic little buggers can be.] That said, If this falls through, I may remake this idea as a much more broad RP that focuses on whoever those involve like the idea of it starting with the most... I just want to try 'this' first... For 'now' suggestions for new crossovers to add to this RP will be considered separate from our starting point [though some things may lead to us using them sooner than later], But, if I remake the RP they will be kept present as options to vote on for the starting point.

And now, starting ideas. I have a few I came up with, but I'm open to the ideas of anyone interested as well, i'm not too prideful to accept if someone presents a better idea than my own... But please, PLEASE, If you're going to join, express interest in a specific idea mentioned below or make a suggestion, if you just plop 'interested' in a post I'm not going to take your interest seriously because it tells me you didn't read this or don't really care enough to make a choice... being that mass effect themes are heavily 'choice' based, that's not a good state of mind =P

1. The Galactic Civilization takes notice of these rising species, analyze, and choose to send someone to 'meet' the ones that are deemed civil enough to have peaceful contact with... Essentially, This one entails the ponies reaching a successful level of space travel sufficient enough to catch the attention of the Galactic Council and an unknown ship arrives to introduce them to the council and... well, do stuff XD There's plenty of room for other events to take place while this is happening to stir up trouble.

2. The now space faring ponies have discovered a massive structure in their system [one of the new relays] and sent a new ship [flag ship? research vessel? experimental?] to investigate and learn about it... In the process of attempting to access it, it is accidentally activated, resulting in the ship involved being inexplicably propelled into the vicinity of the Citadel station [or perhaps some other location we decide on as a group] and the expect-able chaos of an unknown vessel using the Relay network ensues.

3. Naturally, with the Galaxy barely reaching a stable state even after all this time, there's going to be those nasty little groups working under the radar, in the shadows, so on and so forth... and of course there will be those looking to take advantage of these unique species that have not yet been acknowledged as 'having the rights of a galactic civilization'. The one involves a military grade ship pursuing an unknown vessel that is known to have abducted a number of ponies or other races for who knows what reasons [could be a new replacement for cerberus, pirates, or even simple black marketeers seeking to make a fad payday off of these strange little horses that seems to have all kinds of special stuff about them.] It could also include the players being amongst the prisoners being taken elsewhere, the pursuing crew, or both at once.

Oh, and one important thing about this that i'd like opinions on, I am on the fence about this particular piece of pony stuff

Magic, how shall it function in this RP? I have several theories, related or not to mass effecting it, that I'd like to hear some preferences on, and as always i'm open to suggestions or theories from others, though ultimately, unless nobody says 'anything' about it, the ultimate choice is up to the group involved in the RP.

will power = Magic - Magic is the manifestation of sheer will power of an individual, generally related or limited in some way to that individuals natural abilities, and allows for a sudden boost in ability in times of desperation. Essentially, The focus on will is the difference being sending an earth pony into the wall, and being able to stop a Krogan charging at him head-on, or the difference between a unicorn launching an arcane bolt and launching an explosive ball of energy equivalent to a grenade.

Eezo mode - Essentially re-explains Magic as Asari level Biotic ability that is focused in different ways based on pony race, such as pegasi projecting natural 'negative gravity fields' on their own bodies to fly, Earth ponies instinctually projecting skin tight biotic shields to resist attack, and so on.

Skill mode - Magic, though commonly considered a unicorn thing, 'can' also be channeled and cast through Earth pony hooves or Pegasus wings, and perhaps used by other creatures as well, It's simply a matter of re-discovering the methods of channeling magic in a way that is functional for that species [in this RP it'd already have been done], though the varieties of magic are still focused on that individuals natural abilites and racial expectaction [I.e. one Earth pony might be able to gain immense strength through magically enhanced strikes, another might be able to Command stone as long as he keeps his hooves on the ground, a Pegasus might be able to produce lightning or manipulate temperature in the atmosphere through their wings.]

fudge it - Basically this is the version were we all say 'It's magic, nobody understands, we just use it' and go with that.

A Couple of simple rules to keep in mind:
This is in casual for a reason, If you can't meet 'casual' standards, I am obligated as the GM of this RP to hold it against you, much as I hate to do so, I've been 'too nice' in the past and it's bitten me in the ass way too often.

Language - I'm not picky about language, you can be as vulgar, ponificated, or even lewd as you like, even as a pony, as far as I'm concerned a word is a word and if you take offense to someone liking to use certain words, you're a word bigot and Twilight Sparkle will 'BOOK' you for thinking you can tell people what words are allowed to be spoken.

Violence - this is mass effect, blood is common, gore is possible, things explode, people get eaten, people and ponies can and may die, shit happens... That said, don't go 'freddy kruger' on anyone, there may be some villains that show up like that, but it's all circumstantial.

Don't hijack or derail the RP! - This is meant to be a balance RP, we'll be interacting with eachother, fighting, exploring, learning, making decisions as a group or not, we do this 'together'. You're free to make an awesome character and everything, but don't do anything that'll drive the RP away from the theme of being played by a 'group' of individuals. [and no royalty!... I might allow alicorns and other such rare species to be used, but I won't accept characters who's inherent importance would itself derail the RP... that said, you are free to make suggestions for NPCs of such rank, I can always use Codec information =D]

Now then, all this said, Nothing is 'impossible' in this RP, there 'is' 'extremely unlikely' which will be left up to the consensus of the group instead of just my own opinion.