Thanks for reviving the topic for me (Tarakava Nui looks so weird btw)! I've been wanting to share my thoughts on some other combiners I had for a while!
First up are the Ghekula and the Dikapi (yes all of them have "wrong" colours, but I don't care). I think it's pretty obvious what they're supposed to represent; a frog/toad and an emu of sorts. I like how the Dikapi uses the yellow brain-stalk to represent a beak. I also find it pretty comical how large the Ghekula is...
...large enough to devour the Dikapi I imagine! Yes, they surprisingly have functions; simple yet effective ones at that. Push up on the spike attached to the Ghekula's side, and his lower jaw extends downward like Pacman. It'll snap right back when you let go due to a rubber band around it.
As for the Dikapi...eh. You move one of the geared "wings" down and the head swivels around. It's alright, but hard to work with due to the lack of friction.
I also want to look at my favourite 2004 combiner; the Kraawa. When I first saw it, I didn't think it would look as good as the Krahli, with all the gaps and awkward limbs but once I built it, I fell in love with it! I think the designers took inspiration from a brachiosaurus or a giraffe, as one can tell with the long neck and quadrupedal stance.
Speaking of the neck, turn the knob on the back, and it tips downwards, as if its feeding on some shrubs or drinking some water.
Of course, if it wanted to reach leaves from a tall tree (or perhaps intimidate a predator), it can rear up on its hind legs with surprising ease [insert jurassic park music here]. I admit, it's not perfect, but i'm impressed with the overall unique look.
Finally, I'd like to review a 2005 combiner that I just recently built; the Chute Lurker. Looks a lot better in person than in the promotional pics i'd say. It's basically a Visorak centaur...nothing much else to say
One issue I have is how top heavy it is due to the head slouched forward, making posing a bit of a hassle, with the skinny front legs constantly giving out as a result of the weight. (It fell over 4 times while trying to get it in this walking pose)!
It's pretty solid overall though. Better than the two-headed Gate Guardian combi, which i've also built, but shortly took apart to build this instead. So it you're bored with your old Visorak sets such that you're just stuffing them to the edge of your display like @Altair is doing here, build this nifty guy.