Editing Tier System (section)

==Tier 0==
Not in the original list but often mentioned is a "Tier 0". Tier 0 is unique in that it applies to builds, albeit broad ones, not base classes. The primary idea is that while Tier 1 still needs to select what spells he prepares ahead of time, Tier 0 can pull the needed ability out of his ass when he sees a problem. The classic example is the "Rainbow Warsnake", a [[Warmage]] (traditionally, but [[Dread Necromancer]] and [[Beguiler]] also work) that adds the entire Cleric list, core and splat, to his spell list by taking 10 levels of Rainbow Servant. Since for a Warmage his "spell list is the same as his spells known list" he can just cast any spell on the Cleric list spontaneously to deal with problems as they come up. 

Pathfinder briefly had Tier 0 Sorcerer and Oracle via the spell Paragon Surge. Paragon Surge grants the user a feat, chosen when the spell is cast. This feat could be spent on Expanded Arcana, which gave you an extra spell known of your highest level or two of a lower level. This meant a Sorcerer or Oracle could know ''any'' on list spell the player wanted to at the cost of a standard action and third level spell slot (or swift and 7th/metamagic rod and 3rd). This naturally got nerfed and now any future castings the same day give you the same feat. Still potent, and possibly enough to make the gap to tier 1, but not as stupidly broken.

Potentially still Tier 0 in Pathfinder is the Sorcerer archetype Razmiran Priest. This archetype is capable of casting single use magic items of divine spells without expending them by blowing their own spell slots. This allows them to get as wide a spell list as an [[Archivist]], able to cast any divine spell they have a scroll or 1 charge wand of, but cast each spell whenever they want. This requires a Use Magic Device check, but it's piss easy to get it to the point you pass even on a roll of 1. This archetype is generally kept in check by its fluff, which requires being mutated by a crazy evil wizard pretending to be a god.