Dangerous Caves is the gameplay-addition plugin for Bukkit servers. Plugin contains many new special mobs with its own characteristics. Also DC adds a bunch of interesting gameplay features, such as cave ins, depth hypoxia and more.

It's not just a fix for latest versions. DC2 is a fork of DC which provides significant optimizations to the original plugin. Actually plugin was almost fully re-coded from scratch.
Also many thing are configurable now - not just chances to spawn as it was before.

Plugin Link:

https://www.spigotmc.org/resources/dangerous-caves-2-make-your-caves-scary-1-12-2-1-16-3.76212/

Donate:

https://www.buymeacoffee.com/imdanix