Myth-wise:
Heimdall and Loki are the ones who die simultaneously. Fenrir just eats Odin, then is slain by Vidar.
Hati is the one who devours the moon while Skoll devours the sun, though some interpretations attribute one or both to Fenrir.
As for size, Fenrir's saliva after he was trapped via Gleipnir created a river, and when he breaks free his lower jaw touches the sun and his upper jaw the sky. So pretty huge, but unquantifiably so.
Ragnarok did happen though and then the universe was created anew; it's all a giant cycle in Norse mythology is it not? So Fenrir did do all those things. And my money's also on Fenrir.
I'm not sure it really matters. I mean, we generally disregard a lot of narrative in favour of the actual substance of feats. I'd say it doesn't matter how big the Norse thought the moon was if they were talking about that grey thing in the night sky. It just means they were wrong, and that happens with modern writers plenty, particularly when it comes to speed feats.Though I can't remember how large the Norse thought the moon was, so I don't know how impressive that great is.
I am a mighty wizard from magic lands
Isn't classic Fenrir big enough to swallow an entire celestial body whole?
Fenrir is a Kaiju sized wolf who could block out the Sun.
Cerebus is more like the size of a dire wolf or with. Big enough to be rode on, just not that impressive. So yeah, curb STOMP.
Yeah, Cerberus is outclassed here.
Loki seriously has some messed up kids, doesn't he? A kaiju-sized wolf, a serpent that can wrap itself around the whole World, and the queen of the underworld.
That he was the mother of. Because he had sex with another horse as a mare due to the Norse Gods not wanting to pay the horse's owner for building the walls of Asgard. So essentially Loki got impregnated by a horse because his fellow Gods were too cheap to pay a guy what he was legit owed. And then his dad took said horse child as his personal mount while chaining down his other sons whom he couldn't ride and forcing his daughter to work with the dead who didn't get into Valhalla.
Is it any wonder they snapped and went evil?
Critics who treat adult as a term of approval, instead of as a merely descriptive term, cannot be adult themselves. To be concerned about being grown up, to admire the grown up because it is grown up, to blush at the suspicion of being childish; these things are the marks of childhood and adolescence.
- C.S. Lewis
Also Loki in myths is not related at all to Odin aside oath brother. But that's another mess all together.
Bump Definitely Fenris so feared the Gods had to trick him into chains and Tyr had to sacrifice his hand to do so.