I really like the designs of these characters! They're very cute and colorful.

They look a little blurry on my end, though. In the future, I recommend exporting pixel art images at an exact multiple of their original size (5x or 10x usually works for me), and using nearest-neighbor scaling. This should make the sprites much sharper. I've never used IbisPaint before, so I unfortunately can't help you beyond that.

Still, great character designs! I like how round and friendly they look.

I used to be obsessed with the Pingas meme, haha.

The expressions are perfect here! Great job capturing Robotnik's dastardly cunning genius! Scratch and Grounder also look great. Nice work!

I LOVE the dynamic angle here! The curved road is such an awesome perspective, and it adds so much depth to the piece! Sonic is full of action in this piece; his facial expression is conveyed very well, and the curved shoe is very slick. I love how you made Eggman's eyes and teeth kind of glow; it reminds me of the silhouette Eggman moments from the comics.

How long did the shading take you? Because it really paid off! The city's lights are so beautiful, and I love the gradient on the road. The smoke from where the laser hit the road is also a great touch. Everything about this piece is just perfect... How did you do it?! I must know your secrets!!! AAAAAHHH!!!!!

Seriously though, great job all around. I would rate this 6/5 stars if I could.