Mazer with key item.

[orangeangel]

What trigger makes it so that when the hero(example:demon hunter)opens the door when he gets to it?

[Prepare2Lose]

Make a region in front of the gate (where the unit will go to open it). Make the item where you want it. Now make this trigger:
Events
Unit - A unit enters Region 000 <gen>
Conditions
(Triggering unit) Equal to Demon Hunter 0001 <gen>
(Item carried by Demon Hunter 0001 <gen> in slot 1) Equal to Blood Key 0078 <gen>
Actions
Item - Remove Blood Key 0078 <gen>
Destructible - Open Gate (Vertical) 0016 <gen>
*Region 000 is the region in front of the gate
**Demon Hunter 0001 is Player 1's unit
***Blood Key 0078 is the item that opens the gate
****Gate (Vertical) 0016 is the gate you want to open
*****You would have to make a trigger for each player, make this same trigger except change Demon Hunter 0001 to player 2's demon hunter, then player 3's demon hunter, etc.

That is if he has an item. If you want it to open it without any item or anything use this:

Events
Unit - A unit enters Region 000 <gen>
Conditions
Unit Type of (triggering unit) is equal to Demon Hunter
Actions
Destructible - Open Gate (Vertical) 0016 <gen>

[orangeangel]

Ty prep you always help alot, But how do i get (Item carried by Demon Hunter 0001 <gen> in slot 1) Equal to Blood Key 0078 <gen>

[Prepare2Lose]

Its a condition called Item Comparison.
Substitute Blood Key with the item you want to use.