Integrated Dungeons and Structures (aka IDAS) is a mod that adds heavily detailed structures using blocks and mobs from Quark, Supplementaries, Alex’s Mobs, and Create.
Adds boss bars to different mini-bosses (or bosses that lack their own) from numerous different Minecraft mods, including vanilla's Elder Guardian and Warden.
One mixin mod that makes all structures (including non-vanilla ones) more spread out (essentially making them rarer). Useful for big modpacks with lots of structure mods to make exploration more challenging/less repetitive.
Yet Another World Protector, or YAWP for short, is a server-side mod which allows you to protect your creations against various different events/actions of players, mobs and the environment.