How can I make the boss teleport to the player?

There is a procedure block that says "For each entity as (entity iterator) at x y z in a square cube with size (4)". Change the 4 for a bigger number that you think would cover the reach of the enemy. 

Inside that block, you are going to put "Attempt to make (Event/target entity) find path and move to x y z with speed factor (1)", except that you are going to change the x y and z blocks for "X position of (Entity Iterator)" "Y position of (Entity Iterator)" and "Z position of (Entity Iterator)" respectively. Also change the speed if you want it to move faster. 

I think that should do the trick.