I'm trying to add airguard to joe, and so since it is in common1, I don't know why he doesn't have a air guard, help is appreciated.
The engine allows characters the ability to air guard by default. The only way a character cannot air guard is if it's deliberately coded into the character to be disabled. Check for statedef -1,-2 or -3 to find an assertspecial that disallows air guarding or a changestate/selfstate that forces into a different state out of the guard states in the character.