TEMPORARY NOTICE: Due to the game losing its appeal after having used Wonder Trade, I've decided to start a new game. I did keep my old save file and will trade the critters from the list below the moment I get them during my new playthrough, but it'll take a while until I can breed again.
While I keep reading that no Pokémon is going to be mutually exclusive with others in the long run, the temporary exclusivity makes me want to scratch that collector's itch via trading. Also, not every critter that's mutually exclusive with at least one other can be acquired later on yet. That was reason enough for me to open up a trading thread where I show what I have (as in can breed for you) and am looking for.
As I play through the game, this list will grow as I encounter more mutually exclusive Pokémon, if there actually are any. I don't know since this is my first playthrough!
I'm also trying to find all event Pokémon and catch all the wild ones available. If you are interested in one of those that I could already have, just make me an offer. For that purpose, I'll keep the current state of my playthrough at the bottom of this post; I count the proper gym battles, not the badges.
I can't promise much in the way of egg moves (yet), but breeding a specific gender is easy enough. Natures may be more tricky since I don't have a decent stock for nature breeding yet. However, what I'll definitely leave up to chance is shininess; I won't breed shinies for you.
In return, offer me whatever you want, even if it's just the regular old Pidgey or Rattata. Right now, I own everything from the list, but should it expand again, I'd be happy about anything I don't own yet. Otherwise, I appreciate 6IV Pokémon I don't have yet as 6IV and the usual rare items. If you request something specific (like 6IV, which still takes some time even for the turquoise ones), I might ask you for one of the latter three.
Since I'm doing this for the fun and mutual benefit of it, my reaction time depends on my real life situation, but I'll try to check and trade frequently. On a related note, so you have an idea when it's likely for me to be around, my time zone is UTC +1.
But now, finally, the list:
Color code
owned, can breed 5-6 IV with relative ease
owned, can breed
owned, not yet ready to breed
not owned
Starters
Bulbasaur, Charmander, Chespin, Chikorita, Chimchar, Cyndaquil, Fennekin, Froakie, Mudkip, Oshawott, Piplup, Snivy, Squirtle, Tepig, Torchic, Totodile, Treecko, Turtwig
Before First Gym
Pachirisu <-> Zigzagoon
Wingull <-> Panpour
Before Second Gym
Ducklett <-> Drowzee
Cacnea <-> Seel
Before Third Gym (Mystery Egg)
Axew, Azurill, Cottonee, Drilbur, Elekid, Frillish, Larvesta, Pawniard, Phantump, Rhyhorn, Shroomish, Sneasel, Starly, Staryu, Tentacool, Togepi, Vullaby, Vulpix
Before Fourth Gym
Ponyta, Carvanha <-> Buizel, Houndour
Before Fifth Gym
Lunatone <-> Solrock
Playthrough State: just starting out.