Here are some things I'd change to make the badniks feel a bit more lively:
1. Revamping the Crawla
He's fine the way he is right now, but a small change in behavior could benefit the fella a lot. Seeing those circular pillars at the opening area of GFZ1 gave me the idea for Things called Crawla Tracks/Roads: they force a crawla (or a group of them) to crawl along those looping tracks as long as a player isn't around. Basically their movement pattern if they're not bothered. When a player comes close, all crawlas on a track will be alerted at once to enter their active phase simultaneously.
Once they spot a player (a small visual cue could be added alongside this, like his antenna lifting a bit while he faces toward the player before giving chase?), they should leave the tracks and move toward him at a >faster< rate than what they do now (since the player actually knows they're coming!), and keep the chase until they're defeated. It obviously shouldn't be Lance-a-bot fast, but don't make it a slow chase. There's actual action happening with Crawlas now!
To accompany this, maybe smoke could come out of their rear to show that they're actively chasing you until they get beaten down?
The Crawla tracks should be gray, maybe a bit darker than the Crawla's feet thingies, and placed a bit more strategically around the map instead of sporradically like they are now. A cool thing I thought of was making an infinity-shaped track with three Crawlas under the heart emblem area in GFZ1.
Of course, that comes with its downsides - like the first corridor in GFZ2 either being full of these or being void of enemies, but that just goes to show how that first area is so obnoxiously filled with Crawlas. Maybe some decoration and adding the butterfly enemies could help liven it up a bit?
2. Visual effects on the Buzz
Something super simple to do, actually. The buzzing noise is okay, but make their chasing a bit different! They're too boring the way they currently are. Make their acceleration rate work similarly to the BASH, where they actually take some time to enter full speed. Maybe the buzzing's pitch and speed could also increase based on their speed? I'd also kill for a movement trail similar to
the Manta Ray's trail in Super Mario 64, which could also have their own sound effects.
3. Red variants
Probably the single coolest pattern for badniks. If they're red, they're more dangerous. The spincushion from ERZ is literally born from this relationship between the color red and an improvement. When he's red, he's more dangerous! Right now, the differences between normal and red badniks are just "red's faster", but it could be more than that!
-Crawla:
Additionally, maybe the Red Crawlas could have a lazy little projectile like the Crabmeat's in Sonic 1.
I'm absolutely for this. Giving players projectiles to avoid would be super neat
and prepare them for GFZ3! Alongside being faster, the Red Crawla would, instead of bumping into you, stop after getting within a certain radius and start firing bullets from its cannon mouth. Thinking about it, Crawlas are the perfect badniks for firing bullets,
they have a cannon mouth!
-Buzz: Instead of chasing you at a set speed, make the Red Buzz skyrocket toward you really fast, in a similar vein to Tails's Buzz Sentry in Cobalt's Battlemod! A nice change of pace for a badnik that isn't quite used to it's fullest potential. And, of course, a different visual effect/trail to show that it's different.
-Robo-Hood: Getting into fanmade territory, have red robohoods fire a set of three arrows! I've seen some archers do this in other games, it's pretty cool.
-SDURF: Not really more dangerous but I but the SDURF at the end to show that a red variant is really just a change of pace; have this version travel alongside a set arc, like some people on this thread already asked for. It's a perfect excuse to showcase red enemies' difference from regular ones, especially since that'd mean all GFZ badniks would have a red counterpart.
4. Sprites
Oh, sprites. Oh, Jet Jaw from 2.0 that doesn't give me a rest.
Update the sprites on the badniks that need it. Seriously, putting a Jet Jaw and a Crushstacean together makes them feel like they're from different dimensions yet they're from the same zone.
I'm out of ideas now.