Mythic Alliances:

1) Find the Mythic NPC room in the mythic caves.  (Location is random so I can't tell you.)
2) Say the opposing animal's name to the NPC.  Opposition list is below.
3) They will give you tasks.  You must slay three each of both the bosses without killing anything else and bring them certain items.  (I don't know them all.)
4) Complete the tasks, return to the npc, and say the opposing name again.
IMPORTANT: If you have ever spoken to an NPC, do NOT speak to the opposing one.  They'll smite you.  Also, always say yes to the alliance or be smitten.

Rabbit <=> Rooster
Monkey <=> Tiger
Dog <=> Dragon
Horse <=> Rat
Ox <=> Sheep
Pig <=> Snake

Slay 3 Of Each <Foe> Boss ((Total 2 Mythics Per Cave))
Rabbit: Slay Roosters 3 Key to Heaven x8 | Tao stone x4
Rooster: Slay Rabbits 3 Key to Earth x8 | Lucky coin x4
Monkey: Slay Tigers 3 Baekho Key x4 | Purified water x4
Tiger: Slay Monkey 3 Key to Fire x8 | Battle helm x4
Dog: Slay Dragons 3 Chung ryong Key x3 | Dragon's liver x3
Dragon: Slay Dogs 3 Key to Wind x8 | Fragile rose x4
Horse: Slay Rats 3 Key to Pond x8 | Ambrosia x4
Rat: Slay Horse 3 Key to Thunder x8 | Pearl charm x4
Snake: Slay Pig 3 Key to Mountain x8 | Magical dust x4
Pig: Slay Snake 3 Hyun moo Key x4 | Scribe's book x4
Ox: Slay Sheep 3 Ju jak Key x4 | Lucky silver coin x4