Nice to meet you!
Oh darn, I did use those griffon pieces for a recent contest, ah well... 
Hi Malette. Thanks for sharing your work, you have a great start on your portfolio. Your style is cohesive, you have good variety, and I love your characters- they are attractive and approachable.
It's harder to critique someone at your level, because things become less about the fundamentals and more about objective stylistic choices, but I'll give some thoughts on how I personally think you could improve.
First, I agree with what @Kevin-Longueil has said. . . especially his remarks about saturation and value.
Second, I feel that overall, you would benefit from studies on how to portray different materials. I know you are simplifying and stylizing a bit, but I still think that you could distinguish between materials more effectively and make them feel more believable- not necessarily hyper-realistic- but more believable in the style language you have created, if that makes sense.
One example would be in the way you portray fabric and hair. I'm seeing a tendency to over complicate and over emphasize the folds in your fabrics and hair. To me, this tends to distract from the piece as a whole. I think if you simplify the folds, and make some of the folds lighter, it would make for a stronger rendering.
Another thing I'm seeing is that you perhaps don't distinguish enough between reflective surfaces and matte surfaces quite enough. I feel your metal would feel more like metal if you introduced some darker tones from the environment and add stronger highlights. Same goes for something that is slightly more reflective, like a dragon vs a unicorn. I imagine a dragon's skin to be harder and more reflective than a unicorn's. In your piece below, you've shown a nice texture on the dragon that distinguishes it from the smoother nature of a unicorn, but to me it looks like they could almost be made of the same material, because you've rendered the forms in a similar way with a similar value structure. To make something feel harder and shiner, you need to take advantage of adding some highlights to the different forms on it where the light might catch. I've attempted to add more reflected light to my paintover in the dragon and added a dark strip to the sword, but I think it could be pushed further.
One last thing to be aware of is keeping you stylistic choices more consistent. For example in your piece below, I think you could unify some of you style choices. Two of your figures, the guy with the arm sling and the girl have outlines on their shirts that are darker versions of their shirt color, but the guy with the button up shirt has bold, black outlines. Also, on most of your objects, you have outlined the shadow side , but not so much on the egg. I feel if you added a darker outline on the shadow side of the egg and on the jagged pieces of it breaking apart, it would be more consistent with the style you've established and it will help the egg stand out more.
Well, those are some of my thoughts. You should be very proud of your portfolio thus far. Your style will only get stronger with the more pieces you produce. Good luck!