Too intelligent in most versions of D&D.Yeti
Definitely too intelligent (and powerful) in 5E.Kraken
Way too powerful.Terrasque
Divine beings and way too powerful.Cerberus
Femrir
none of those are simple beasts they're generally too intelligent and Cerberus and Fenrir are outright celestial. The Tarrasque is a unique being closer to Dragon than beast (if it were me I'd create a Kaiju category)What about
Yeti
Kraken
Terrasque
Cerberus
Femrir
Winter wolves have a cold breath, feels a bit too magical for a beastOwlbear, Griffon, Tressym, Winter wolf, Guardian wolf, Girallons, Cave fisher, Decapus, Gorgon Bull, Sealion and Hippocampus, Ankheg, Remorhaz, Carrion Crawler, Worms and Slugs etc
Displacer Beast, Catoblepas, Leucrotta, Cockatrice, Basilisk I'd categorize as Fey Beasts
Winter wolf is just a dire wolf with an elemental enhancement, to me thats 'naturally' occurring in a high magic world, especially with Druids getting elemental forms at high levelsWinter wolves have a cold breath, feels a bit too magical for a beast
There are real-life animals with even more powerful venom.Carrion crawler isn't one I'd allow -- that paralyzation is so good, it's arguably magical.