THE LOST POKEMON
This is a very brief compilation of the Beta and unreleased Pokemon we know to date, of course there are missing some, but I tried to draw the most important ones here.
I will add a little resume of what I think of them:
Torchic: I don't think it changes too much, but I'm starting to think the Blaziken we got, is the evolution of this beta version because of this ear-things on Torchic transforming into the 'hair' or 'feathers' Blaziken actually has...
Bukū: I think it's not a beta Qwilfish, I like to think it was a possible pre-evo, because it looks really cute.
Honoguma (Firebear): the beta fire starter of the demo Gold and Silver versions, I personally like it more than Cyndaquil.
Happa: Beta Chikorita with 'ear-things', I like it more than the official Chikorita.
Pikachu: to me, this one looks cuter, but I like the normal one more.
As I've said before, I like to think this early Marill was designed to be a normal type Pokemon like Jigglypuff or Clefairy, but then someone thought it was a cool idea to make it a water type. I'd like to see it released even as a female variant now.
Kurusu: I really love this unreleased Pokemon, some time ago I used to think this was an unreleased Lapras' pre-evo, but nah, this was the original water starter of Gen II.
'Peritop': There is really no info on this one, but some say it's a beta Hitmontop; what I think, is that this was an original top Pokemon, but somehow another designer thought it was a good idea to make a Tyrogue evo based on a 'top' and kapoeira, and they rejected this one because if they had released it, it would've been too similar to Hitmontop.
Kangaskhan's baby: I like to call it 'Kanjoey' haha don't steal my name! I'm sure I haven't seen it before.
I counted it as an unreleased Pokemon, because I see it as one, come on, this baby could easily be an official Kangaskhan pre evo.
Treecko: I like the official one way more, but this looks more like Grovyle.
Girafarig: I tried to slightly redesign it, and I liked the result.
Ledyba: I also redesigned this one, you can watch my full version here: [link]
I think I made the most truthful fan art of this unreleased turtle, I also named it Laketoise, but there is no info on this one.
Shellder (Spiral Forme): Even if you don't count this one as a beta Pokemon, I've always seen it as the first 'forme', and I'd love it to be released some day.
Gastrodon: I think it should have another color but I did not wanted to drastically change it, and I think this one was the original Gastrodon that was going to be released along with Shellos on Gen III.
'Blaztias': Some say this one was a Pokemon itself and then the designers separated it into Blaziken and Latias, but, could this be the proof that Game Freak at some point considered to fuse the Pokemon? I don't know...
Tyranitar: I don't like it
Lapras: I'd like to see it as a male variant of the current Lapras.
Well, after that long description, I will just post some links so you can know more about this kind of stuff.