You asked for a critique? You've got one. I'm not the butt-kissing kind of critic, so brace yourself and I hope I don't sound overly harsh!
I'll start with anatomy. Anatomy is an evil, evil thing when you're drawing ponies, because it's very oversimplified and therefore very easy to overlook. Since each pony has his/her own little kinks, I'll break these dudes down one by one.
Venom Milly's pose is very awkward. The way her arms (legs?) are positioned is anatomically impossible. Keep in mind that horses have shoulders too and the way a horse's (and human's) shoulders are fitted into his torso make it so that the legs have to be framing the head when positioned like that. The only way Milly's arms would be like that is if her legs were attached to her neck. And that's impossible. Her head also looks a bit weird to me...correct me if I'm wrong, but I think if she were to have her head like that, her neck would be broken. I don't think a contortionist could even position their head like that.
Moving on to regular Milly, I have absolutely no idea what she's facing. Is she on the floor? Is she facing the 'wall' in the back of the picture? WE WILL NEVER KNOW. I think she's supposed to have her face on the ground but, with the way she's drawn, the only way this would be possible is if her face were to be flat.
Spidercolt's back leg shouldn't be bent like that. The back legs of a horse naturally move out, because that's how the 'knees' are made to move. His leg is moving backwards. Ouch. Another problem I have is the way his head and body are positioned in relation to each other. His head looks like it's been turned 180°. I don't think even the amazing spider colt could achieve such a feat. When you look behind you, your body will turn with your head. The only animal this rule does not apply to is owls, and we are not drawing owls. And finally, his right back hoof is bigger than the rest.
Finally, Discord Milly. She actually looks pretty good, so I'm not going to spend much time on her.
There are some errors common in all your ponies, which I will touch upon here. I redlined it here so follow along [link]
The red lines denote problems in the neck. You've made your necks too humanlike! They're too short and they don't...flow the way horse necks do. Hopefully that doesn't need much more explanation. Next, the green lines- your noses are a bit flat and not very show-accurate, assuming that's what you're going for. If not, disregard that. The yellow lines show curves where they're not present currently. Finally the blue lines correct the tails. Tails are an extension of the spine, but yours don't look like they're extending from the spine. This is a common error among many artists, including me sometimes if I'm not looking carefully enough. These are minute details but they make your ponies look a lot more convincing, I promise. I'm not too great at explaining these errors, but for a more in depth look at pony anatomy shimmy on over to *Pix3M's tutorials! They help a great deal and can explain much better than I can. [link]
Now that we're out of anatomy I'm going to spend a little bit of time talking about your presentation. I realize you use MSPaint and it's 1. crude and 2. a pain in the rear, but this picture is pretty boring. The thing that stood out most to me was the lack of shading in this piece. Flat colour has its place, but it could easily be eradicated in this picture. It would make it a heck of a lot more pleasing to the eye if you'd have shaded it. Continuing on, the composition on this doesn't seem to be well thought-out. The background is boring, and even if you didn't have a particular story in mind you could have at least added interest. There is nowhere to draw the viewer's eye in. At the very least the colour palette could have been a bit more unified to draw this together as a finished piece. Your colours seem to be the ones Paint offers by default. Don't use those! They're very harsh and not pleasing to the eyes. Try the colour picker. This is a lot of work but it definitely pays off! Another option is a comic strip, which I feel would be more appropriate with this piece because having all three ponies speaking simultaneously is a bit overwhelming. One last thing concerning technique...have you ever tried faking pen pressure in Paint? It's a very useful thing and it makes your drawings look a hell of a lot more professional. Coloured lineart can also make things a bit more palatable, as black can look really harsh when paired with certain colours. Just in case you want to see to believe, I've done two versions of the same drawing, one following the tips I've given you and one disregarding them. See? What a difference just a little bit of work makes! [link]
Your work isn't bad for only 6 months of practice! Just keep working towards improvement and doing what you love. Practice makes proficient! Also, sorry for the excessively long critique, I'm just a really detail oriented person and I like to go in depth on everything.
Woman, you are the queen of critiques! XD I'm still trying to read that all~ But thanks! I'm still an artist in training and will take this help to heart! Thanks again <3
Oh my goodness that's great! I thought I was being harsh, but then again, no improvement can come from dousing one in nothing but praise. xD Just keep at it and I'm sure you'll get a heck of a lot better!