Hey!

The best pathfinding around here is the one made by Superku. It will will satisfy your needs. As for following player around, in elevators, stairs etc, it's all up to you, how you would create it based on his pathfinding solution. Intense X isn't alive anymore. There is one forum member (Alibaba), he used to work with it's source, you could ask him for help, but I'd rather created my own solution based on Superku's pathfinding.

Greets.