Took a screenshot.
Basically a giant adamantoise. It was seen in the past benchmark, but I think Yoshi mentioned in an interview that something to that scale wouldn't actually be in the game. So perhaps a dash to those hoping for world bosses.
If that's what you thought when I in particular was mentioning world bosses, then we weren't on the same page. I certainly didn't have mega-bosses like that in mind, I was thinking more along the lines of HNM type monsters (without the 24 hour camp times.) Bosses that anyone could claim... not just those living on their computer.
Additionally, how could you NOT want something that awesome in the game?
I'm for big enemies, but if perspective is properly considered, running a circle around such a mob would probably take a couple minutes. So, while I could see a fight like this where its broken into 5 targets (4 legs you have to take down before the head), I'm not sure colossus-type mobs work well in the MMO genre. From there, let's realistically consider what kind of attacks a mob of this size would pull off. The legs would assuredly be limited to directional kicks and AoE stomps. Head could have head butts, bites, and probably some breath attacks given this is a model rip from XI. Could maybe have an attack where its head/legs retract and it does a spin in its shell, but in general, scale and our own perspective would have us "too close" to really in take in the potential visceral majesty. Finally, there's just a matter of where you'd put such giant things alongside potential immersion issues. It'd almost be like putting a whale in a tank just barely bigger than the whale in a lot of cases without the zone being solely designed for this encounter first.
In the end, I think mobs of Ifrit's scale (I think that's Ifrit in the benchmark) should be the general limit. Again, I'm not against larger segmented fights, but introducing some means to accelerate movement while participating would be a definite plus. My knock on this as a not-world-spawn was because it was simply free roaming alongside Yoshi's past comment and I have no doubt come launch you'll see people asking where the giant turtle is even though the benchmark ripped various assets that wouldn't normally be in a specific location just to offer a bit of pizzazz. And now that I think about it, the potential Bahamut fight may resemble some of the encounters with dragons from GW2 (which will be bigger than Ifrit). I just hope SE does 'em better.