Ok, so here are some advice I can give you:
-More anatomy practices (from the pieces you just posted: the jaws of the characters are too big, mouth and nose are too far away and so are the eyes in some pieces->especially in the first two and last pics)
-The perspectives are off especially on the Mikey drawing. You were going for a head-tilted-up look, right? Because the upper half of the face looks like that (until the nose ) but the lower half looks like a flat angle. It's giving me a weird vibe.
-The way you draw guys is pretty feminine. The shoulders are narrow at times and the neck is too thin for a male. Sure there are guys with more feminine features but the characters you draw are ninjas who basically trained in their whole life so it's fair to assume they'd be more muscular (not beefcakes tho).
-This is just my nitpick but the outfits and hairstyles doesn't really match the characters.
Sorry if it's not a lot or too helpful, I'm not in my best shape rn but I hope I gave you some good advice.