Cobblemon: Legends Untold

This datapack/mod expands Cobblemon by adding 8 legendary and 1 mythical Pokémon, 5 unique structures, and 7 new items.
Important note: When using the datapack version, place the file in both the resource pack folder and datapack folder. When updating your world, you may need to relocate some structures.
The mod has not been tested on servers - use at your own risk.

Legendary and Mythical Pokémon
Rayquaza

Rayquaza inhabits the Sky Pillar - a rare structure that can be found in mountain biomes. Bringing a Jade Orb to the top of the Sky Pillar will summon a level 70 Rayquaza. In some structures, you may occasionally find a Jade Orb or Jade Map that points directly to the Sky Pillar. Each player on the server gets only one chance to catch Rayquaza.
Mewtwo

In legendary structures like the Sky Pillar, you can sometimes find Mew DNA. Using this item along with a Nether Star or Comet Shard, you can create Mewtwo in a Resurrection Machine.
Mew

Mew hides in the Faraway Ruins - a rare structure found in jungle biomes. Entering the ruins causes a level 30 Mew to appear. In some structures, you may occasionally discover an Old Map that leads directly to the Faraway Ruins. Each player gets only one chance to catch Mew. The ruins' design is inspired by Faraway Island from the third generation of Pokémon.
Xerneas

Xerneas dwells at the Tree of Life - a rare structure in oak forests. Approaching the Tree of Life summons a level 50 Xerneas. Sometimes in structures, you can find a Life Map that shows the way to the Tree of Life. Each player has only one attempt to catch Xerneas. The Tree of Life is based on a location from Pokemon Mystery Dungeon.
Legendary Birds
The Legendary Birds are roaming legendary Pokémon that can randomly appear in any biome, but three times rarer than starter Pokémon. Weather conditions affect their spawn frequency: Articuno appears twice as often during rain, Zapdos during thunderstorms, and Moltres during clear weather.
Walking Wake and Iron Leaves

Walking Wake and Iron Leaves inhabit Tera Dens - underground structures of two types: Water Tera Dens and Psychic Tera Dens. Approaching the center of a den summons the respective legendary Pokémon at level 75: Walking Wake in water dens and Iron Leaves in psychic dens. In some structures, you may occasionally find a Tera Map leading to one of the Tera Dens. Each player gets only one chance to catch them.
Why these particular legendary Pokémon? ¯(ツ)/¯