Added:

-Added two new advancements related to Demogorgon Domestication.

-Added a new advancement for locating your base's reflection in The Upside Down.

-Added a map that charts Underdark tunnels as a debug item.

-Added a limit to the size of tunnels as a gamerule.

Changed:

-Tunnels now all generate all at once across the world using a new backend generation system that doesn't hamper performance.

-Red Lightning now plays the "distant" sound when lightning is 25 blocks away, rather than 100.

-Red Lightning now has more range in which it strikes around the player in The Upside Down.

Fixed:

-Fixed TPS drops when too many Burrow Points exist.

-Fixed tamed Demodogs losing their tamed status when summoned with the bell.