From publisher blurb:
It’s Going to be Colossal!
Kaiju Codex brings you 20 new massive monsters for Game Masters to use in their 5th Edition roleplaying game ranging from the natural disaster style Worldshaker to the lesser Kaiju like the Hubrun, or The Big Goblin, so you can find a challenge to fit your game! This product adds some new twists so you can make the existing Kaiju even more dangerous!
We also includeThe Iron Knight for Player Characters to crew, so you can have Kaiju vs Mech-like combat. There is an artifact for PCs to control a Kaiju for a short period of time, so you can Let Them Fight!
Plus advice on GMing Kaiju so your game can play like a Japanese Monster Movie or focus on something more classical like Jörmungandr, The World Serpent.