Ability Buttons on non-controlled units only available for some players?

[Titanhex]

Alright if you've played the game DotA you know that Naix has an ultimate that lets him go inside his target. He can push a button that's put on the target that only he can push, which lets him exit.

Basically it's a button only a specific player can use, even if it's no on their own units. I imagine it has something to do with shop sharing, but I'm not sure the mechanics and how to make it local. Any help or pointers would be great!

 

[defskull]

You might not noticed this, right ?
Well, when Naix is "inside" a targeted unit, it is actually "hidden" out of sight and creates an SFX only to him and his allied visions.
You see, after you used Infest, when you click on the unit, it is actually "re-directing" your selection to the real Naix, therefore, you're not really "control" that unit, it is actually directs you to select the actual hidden Naix, that's why you can activate the spell.
Also if you notice, the Naix interface when you select the unit, is not creeps' face, right ? It is Naix's, right ?
Well, the Naix's face is not the real Naix, it is only a dummy unit that have the interface of Naix because as you can see the HP of that Naix at that time is around 50,000 whereas you real Naix could not reach that value, right ?
Plus, the "selected" Naix has no items to hold at all, this mean that the unit is truly a Dummy.

So, it is actually the Dummy having that ability to tear out of the unit's body, not the real Naix.

Basically it's a button only a specific player can use

First, it checks who selects the unit, if the selecting player is the owner of that Naix, it directs you to the real Naix.
If not, you just select the unit.
This is to prevent when you are sharing units, you will prevent the wrong re-directing to the false owner.

 

[Titanhex]

Ahh perfect. This is the explanation I was looking for.

I can use this info to do what I was going to do. Though it might be a little more work it should be completely doable now. Thanks!