That's actually a very good question! Mythical sounds good however I'm not 100% sure if this will be the name to the Tier above Legendary.
In FAR, REALLY FAR plan in the game will be fighting system and stats system of course! Also, I'm planning to add to that also clothes, armours, crafting & trading with NPCs. However I'm collecting a party that'll allow me to introduce all of that into the game, but the plans are big and I won't let them go! :)