Kaiju. The monsters that other monsters run from.
Godzilla (King of the Monsters,) King Ghidorah, Destroyah, Mothra, Rhodan, and King Kong- the names alone conjure images of buildings being toppled, entire tank battalions being crushed, an a roar that makes everyone shudder. In movie lore, there are entire islands dedicated to these massive creatures. (No, not just Japan.) There are entire dimensions dedicated to these things. (Pacific Rim.)
They’re a common foe in some tabletop roleplaying games. Power Rangers, for example, has one show up in most episodes (*game sessions.) In superhero games such as ICONS, they are an all-hands-on-deck event just as they are in the comics. But in a fantasy ttrpg? They’re downright terrifying.
There could potentially be kaiju in Dungeons & Dragons or other fantasy TTRPGs that make the Tarrasque look like a litter-trained Dachshund. Pretty sure Godzilla could stomp a Tarrasque into the dirt. (*Just my opinion.) Given the size of a medieval city, I’m pretty sure one kaiju making landfall is going to flatten whatever coastal city it decides to ROFLstomp.
Cripes, even most younger dragons would probably steer clear of Kaiju. Some of the bigger ones might go head-to-head, but the odds are stacked in the Kaiju’s favor. Imagine what a mess a Kaiju sized dragon would make. Entire legions of adventurers would have to be called up just to slow one down.
One final thought when it comes to fantasy Kaiju: if magic is the fantasy equivalent of nuclear energy, why aren’t there more fantasy Kaiju? Supposedly Godzilla came about due to humankind’s experiments with the atom, right? Gojira was nature’s reaction to atomic testing. Why wouldn’t the same apply in high fantasy games?

Thanks for stopping by. I appreciate you. Still getting caught up.