Okay, no, there are many more things I can say:
Why is it round? Why is the picture in the 3e MM even less menacing than the one in the Fiend Folio? I mean, it's kinda menacing. I could see how this thing could be scary. And then I think, "Round bird with four legs what?"
It gives off toxic black smoke when injured. That's actually kinda cool.
I've never used this thing in a game, and never had it inflicted on me in a game. It's in 3e D&D core, so obviously it's out there and around in people's headspace, but I suspect I'm not alone in looking at the picture and going "round bird four legs what?"
Which makes me think, hey, maybe I should use it in a game sometime. It's creepy and otheworldly and evil, it doesn't get much play, and the name is actually kind a cool.
This would all hinge on DM description, naturally. If I just went and introduced it with, "it's a large, round bird, with four legs each ending in wicked claws," well... basically I'd need some other way to describe it than "large, round bird." Even my players would laugh at me, and they're used to every monster description ending with "and it has great, terrible claws!"
Things to start with in describing the Achaierai besides "large, round bird":
- Its stilted, unearthly gate.
- Its four metallic, scaly legs, each ending in a wickedly sharp claw.
- Its long, hooked beak.
- Its terrible, clanging squawk, that seems to echo through the black depths of your very mind.
- Its blood-red, filthy, matted feathers.
- Its roving yellow eyes.
(And funny, I thought this was going to be my first FF post to revolve around some variation of "this is the most ridiculous monster I've ever heard of!" but apparently that fine distinction shall go to another critter. I really do think that this thing is kind of cool, in a deranged sort of way, now that I've given it some thought. And "deranged" is the best way to be cool, if you ask me.)