0x800 Physics Flag
Even if you disable the 0x1 flag for a thing, it will still slide downwards on wall surfaces as if to simulate
gravity. Clearing this flag will allow things to attach to wall surfaces the same way that they attach
to floor surfaces. Using this flag with 0x90 and giving it to a player will allow that player to walk
on wall surfaces without a problem.
Thanks to ZeqMacaw for discovering this.