I find it a bit annoying that when you walk a bit, do something and then undo, you get teleported all the way back. It would be nicer if you would be teleported back to the last valid standing location instead of the first one after the last action. I figure this can be changed by putting the player position onto the undo stack last and swapping it out as long as you are on a valid standing location. Also, touching salvage points should be an undoable action, which it currently isn't. Additionally, there is a bug where, when you did an action but are not in a valid location (like within a salvage point), you can't undo. Also, why do you need recentPush? Isn't recentPush always 1 once you pushed an undo stack frame? I mean, after every undoPOP call you eventually call undoPUSH, so recentPush will necessarily be 1.