Monster Mania

Question: Could the giant, evil monsters of Norse myth like Fenrir, Nidhoggr and Jormungandr be considered Titan Avatars?

Question: Would the Fenris Wolf, Jormungandr and Nidhoggr work as Titan Avatars, maybe of Beasts?

Yes, actually! Scion: Ragnarok even stats Fenrir and Jormungandr as if they were Titan Avatars on page 111, explaining that while they owe allegiance to no Titanrealm they are still basically the same kind of creature. The two of them as Titan Avatars is practically a feature of the game even withou house-ruling. Nidhoggr, whose stats are in Scion: Demigod on page 233, gets the short end of the stick in the original line where he has for some reason been demoted to about Legend 7, but if you want to increase his power level, ain't nobody here going to tell you not to.

While we're not sure we want to introduce the idea of Titan Avatars who don't have a realm, since that's something of a contradiction in terms and they'd probably be better off as just gods or very powerful Typhonian beasts, we're all about Fenrir and Jormungandr as Titan Avatars when attached to a realm. We'd likely consider them to be possible representatives of Emamu, the Titanrealm of Beasts that opposes the Anunna, possibly with their terrible mother Angrboda.

Nidhoggr, who has less of a fancy role to play, we might consider just an insanely large and powerful Typhonian beast, but it really depends on the flavor you want to run with. One thing he's definitely not is Legend 7, so make him as badass as your game and heart desire!