The Tippyverse. The biggest mechanical conceits were permanent Teleportation Cirlces, together with resetting traps that created food and water. And of course, RAW on the cost to create magic items based on spell level, combined with fairly-available shenanigans that trivialized gold as a resource. (If you can chain-bind efreets etc, you can create arbitrary amounts of gold, which makes your magic item creation effectively free.)
In Emperor Tippy's own words....
https://forums.giantitp.com/showthre...-Emperor-Tippy