Turn active object into an obstacle and Walking through walls

I have two questions
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first of all:

I'm trying to create an obstacle out of an active object instead of a backdrop.

The problem is that the obstacle doesn't stop the character's movement completely. I dont know how to explain it, but half of the obstacle actually stops the character's movement, but the character can go through the other half of it as if it didnt exist.

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Also at the same time I'm trying to create an ability that when the player presses a key on the keyboard like "ctrl", they turn invisible and can walk through walls.

I tried to set it up so that the alterable value of the character is always 0, THEN when the player presses the "ctrl" key it adds 1 to the character's alterable value.

When the character's alterable value is 0 the character is visible and shouldn't be able to go through walls, but when the character's alterable value is 1 the character turns invisible and should be able to go through walls.

I tried pasting the active object obstacle to the background, which works in stopping the movement of the character, but then I couldn't get the character to go through the wall when activating the invisibility ability.

But it doesn't work. I feel like I tried everything.

How do you make an active object into an obstacle? and how can you make it so that when you press a key, the character turns invisible and can go through walls?

You can simply add an action like:

character collides with "active_obstacle"
+character FLAG xx (or alt. val. xx) = off (or 0)
>>> stop

and then

on keypress "I" (make invisible)
>>> set FLAG xx ON (or alt. val. xx to 1)

FLAG xx ON (or alt. val. xx = 1)
>>> make invisible

FLAG xx OFF (or alt. val. xx = 0)
>>> reappear

Awesome thanks =D

For the Issue - Active objects Collision....
I ran in this problem couple times...
Reason is the Collision of the Active object is the SHAPE OF THE FIRST IMAGE spawn in the game... so if you have many frames like appearing animation. . the first frame which is mostly small, is the collision shape...
... that's why it seems like the half of it doesnt exist...
To solve the problem --

maybe set the condition to Always, or activate it within a group, etc...
Add the Action: ANIMATION > ADD BACKDROP >> OBSTACLE

dont use condition: ActiveObstacle Collision with Player

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EDIT POST: You can't delete it since it's now a backdrop? :(
...waiting for another solution

I solved this by having a Group Qualifier .0, and the movement engine always does a check against backdrops and then another check against group qualifier 0 when testing collisions.