I'm horrid at drawing, so I'll critique instead, in a couple on sentences. I'm not an expert or anything, so you can dismiss what I say if you wish. Don't take it the wrong way.
Yilx A is just a Cacturne clone in my opinion, but B and the rejected C (why it's rejected, I don't know) look pretty nice! B's hand-leaf things look a little... Off, though.
Quanyaila I like the concept quite a lot. Basically, a Bisharp mixed with a Roserade. It's a rose, but with a dark monotone and clearly vicious intentions. C'mon, a murderous rose? Who can't like that?
Mos-Quitoxe Um, Wario much? I'm not sure about a garlic mon, and the shading looks a little off, but it definitely has potential. I'd say it's more of a Grass/Poison than Grass/Dark, but that's just me. I can totally see Stench being an ability for this, though.
Birkal A skull-based cob of corn? Interesting. I don't think the purple blends well with the yellow-orange thing, and it's a little more "wide" than I'd imagine it to be, but it's pretty good overall.
Menshay A jester Cacturne is the first thing that comes to mind. Nonetheless, this is pretty neat. The wings and long fingers seem out of place, though.
pkmn-taicho321 Watchog in a Carnivine costume? That's what comes to mind first for me. However, regardless, I like this one. The tail looks really unnatural, though.
elcheeso Hmm... This looks good, but I dislike the design of the scales/leaves on the body. I also think that a bull may not be the best interpretation of Grass/Dark, but that's my opinion, and opinions are made to be biased, so...
paintseagull A dripping swamp mon? I admit, the first thing I though of when I saw Grass/Dark was "swamp." Regardless, this is pretty good. I dislike the general feet area and random dots of colours, and this looks a tad too much like an Eeveelutions to me. It's neat, and a quick rework could make it look great!
Dracoyoshi8 Interesting. Neat concept (we have Houndoom, so why not?) and I like the evil forest-type color scheme, but the leaves should maintain a constant color, not different shades, and the tongue is... Odd. However, this is still neat. Moreover, the brown dots add a nice texture.
Hollymon Well, your name explains it pretty well. I don't think that the trademark plant of Christmas should be associated with darkness, but you executed it pretty well. It looks a little too jolly (no pun intended) for a Dark type, even given the mistletoe theme, but it's still pretty nice.
Chomz Sawsbuck? No offense, but with a theme like that, I doubt it'll be picked. However, you did draw it beautifully- it's just, the Deerling line, and Pokemon X's legendary, and Stantler, and... You get the point. It's a great image with an overdone concept- quite an unfortunate curse.
Arkeis Even though the second reminds me if Watchog, it's still pretty good. I much prefer the Tiki mon, though. It's just... Something about it says "awesome." It looks Dark, it looks Grass, it looks amazing.
zyrefredric Your drawing skills have potential, but it's a little jagged ATM. Still, it's a great concept. Not sure about if the fire helps or hinders the design, though.
Orivexes Picklemon, eh? Neat concept, neat design, neat drawing. The colour scheme just seems a little ugly, but that's just me.
Doran Dragon Tauros Shiftry. Really. Looking past the air of these Pokemon, it's neat, but I don't enjoy the shade of green you chose. It's a great drawing in its own right, though.
Green Dweeb Sorry, Menshay got to the concept first. However, I like the drawing you did. It has that mischievous plant look all over it.
Nastyjungle This is more like Pyroak's kind of typing to me, and, as said before, I don't like the idea of a bull for this (yes, even the Minotaur), but it does look nice. The horns are easily the highlight of the image, beautifully drawn.
ShyGuy1221 Hmm... I like the concept, but I think the color scheme, though clearly showing "Dark" all over it, seems a little out of place. I like the eyes, though.
Steampowered Phew, almost done. Anyways, I like the concept and image, but the body shape is so... Odd. It's also a little too furry for my liking on a Dark type. The facial expression is masterfully done, however.
Chris900 Seems neat and all, but the leaves are a little unnatural. The eyes and concept are both great, and this seems pretty good all in all.
Harle Hmm... I don't enjoy the arms/leaves, but the general concept and facial expressions are great. I enjoy it and all, but it seems a little too... Jagged.
Yilx A is just a Cacturne clone in my opinion, but B and the rejected C (why it's rejected, I don't know) look pretty nice! B's hand-leaf things look a little... Off, though.
Quanyaila I like the concept quite a lot. Basically, a Bisharp mixed with a Roserade. It's a rose, but with a dark monotone and clearly vicious intentions. C'mon, a murderous rose? Who can't like that?
Mos-Quitoxe Um, Wario much? I'm not sure about a garlic mon, and the shading looks a little off, but it definitely has potential. I'd say it's more of a Grass/Poison than Grass/Dark, but that's just me. I can totally see Stench being an ability for this, though.
Birkal A skull-based cob of corn? Interesting. I don't think the purple blends well with the yellow-orange thing, and it's a little more "wide" than I'd imagine it to be, but it's pretty good overall.
Menshay A jester Cacturne is the first thing that comes to mind. Nonetheless, this is pretty neat. The wings and long fingers seem out of place, though.
pkmn-taicho321 Watchog in a Carnivine costume? That's what comes to mind first for me. However, regardless, I like this one. The tail looks really unnatural, though.
elcheeso Hmm... This looks good, but I dislike the design of the scales/leaves on the body. I also think that a bull may not be the best interpretation of Grass/Dark, but that's my opinion, and opinions are made to be biased, so...
paintseagull A dripping swamp mon? I admit, the first thing I though of when I saw Grass/Dark was "swamp." Regardless, this is pretty good. I dislike the general feet area and random dots of colours, and this looks a tad too much like an Eeveelutions to me. It's neat, and a quick rework could make it look great!
Dracoyoshi8 Interesting. Neat concept (we have Houndoom, so why not?) and I like the evil forest-type color scheme, but the leaves should maintain a constant color, not different shades, and the tongue is... Odd. However, this is still neat. Moreover, the brown dots add a nice texture.
Hollymon Well, your name explains it pretty well. I don't think that the trademark plant of Christmas should be associated with darkness, but you executed it pretty well. It looks a little too jolly (no pun intended) for a Dark type, even given the mistletoe theme, but it's still pretty nice.
Chomz Sawsbuck? No offense, but with a theme like that, I doubt it'll be picked. However, you did draw it beautifully- it's just, the Deerling line, and Pokemon X's legendary, and Stantler, and... You get the point. It's a great image with an overdone concept- quite an unfortunate curse.
Arkeis Even though the second reminds me if Watchog, it's still pretty good. I much prefer the Tiki mon, though. It's just... Something about it says "awesome." It looks Dark, it looks Grass, it looks amazing.
zyrefredric Your drawing skills have potential, but it's a little jagged ATM. Still, it's a great concept. Not sure about if the fire helps or hinders the design, though.
Orivexes Picklemon, eh? Neat concept, neat design, neat drawing. The colour scheme just seems a little ugly, but that's just me.
Doran Dragon Tauros Shiftry. Really. Looking past the air of these Pokemon, it's neat, but I don't enjoy the shade of green you chose. It's a great drawing in its own right, though.
Green Dweeb Sorry, Menshay got to the concept first. However, I like the drawing you did. It has that mischievous plant look all over it.
Nastyjungle This is more like Pyroak's kind of typing to me, and, as said before, I don't like the idea of a bull for this (yes, even the Minotaur), but it does look nice. The horns are easily the highlight of the image, beautifully drawn.
ShyGuy1221 Hmm... I like the concept, but I think the color scheme, though clearly showing "Dark" all over it, seems a little out of place. I like the eyes, though.
Steampowered Phew, almost done. Anyways, I like the concept and image, but the body shape is so... Odd. It's also a little too furry for my liking on a Dark type. The facial expression is masterfully done, however.
Chris900 Seems neat and all, but the leaves are a little unnatural. The eyes and concept are both great, and this seems pretty good all in all.
Harle Hmm... I don't enjoy the arms/leaves, but the general concept and facial expressions are great. I enjoy it and all, but it seems a little too... Jagged.