For questions dealing with characters at the very highest levels of power possible in their system.
"Tiers" are used as a description of the various levels of power a character may progress through within a system. "Epic tier" is generally used to refer to the highest such tier.
Characters in the epic tier may have assumed god-like powers in a world of mortals, or may be among a class of powered beings who can only meaningfully interact with each other.
Running an adventure/campaign for epic-tier characters is assumed in some systems to be qualitatively-different in its challenges and techniques than running adventures/campaigns for "regular" characters.
