PrimordialApex

This mod as its summary suggests, adds a large spinosaurus-based apex predator boss named the Velumontesaurus (meaning Mountain Lizard), as its name suggests, it is huge, nearly twice the size of Tremorsaurus, 

It spawns within rock-like structures scattered throughout a new dimension, the primordial realm, where saurian creatures are common and alive (if used with alex's caves, this includes creatures from that mod!). Though, be warned, these creatures are aggressive.

It must first be awakenned by stepping on the block at the central of its cavern. This will spawn the creature.

On death, the creature drops its sail, which when combined with the spikes from its servant mob, the Velumonteraptor, and a wooden sword, can create the Mountain Lizard's blade

REQUIRES GECKOLIB

Heavily recommended to use the mod with Alex's Caves for best experience, although the mod can be used on it's own.

Additionally, there is a "time travelling" feature that can be attained using other portals the mod has to offer, including an even more ancient variant of the earth, and earth after a nuclear apocalypse.

PLEASE NOTE: THIS MOD IS MADE WITH MCREATOR, MEANING I CAN'T MAKE A 1:1 OF ALEX'S CAVES' STYLE

Credit to DevSnako