jeffige , Aphrodite and Katala already covered pretty much everything about this. You have misunderstood what the Platform behavior does and what it does not do and for what purposes it's made for. Let me put it in my words too, just for the sake of argument.
Forget about the animations for a moment. Lets focus on a simple box. How do you make it move..? You can can create 2 events just to make it move left/right:
When right arrow is down---> box set X position to self.X + 350*dt (to move it 350 pix per second like the Platform behavior does)
Equally, When left arrow is down----> box set X position to self.X - 350*dt.
So far so good. But how do you make it accelerate and decelerate to and from this 350 pix per second speed? You''ll need to make some variables that are interpolating from 0 to 350 and 350 to 0 speed. That's a bit complicated but doable.
Now, how do you make it jump? You need a way for it to move on the Y axis in a parabolic manner. I wont even pretend to know the math behind it. That's even harder. But let's say that you did manage to make a system that does that, and even simulate the acceleration from the gravity.
Now you are left with the collision detections. When the box is on the floor, when it has a wall on the right or on the left. This is very-very difficult to make with events. But it comes by default with the Platform behavior.
Having said all of the above, up until now nothing has anything to do with animations. These are events that sorely make a box behave/move like Mario.
If you want animations (visual representations of someone doing something), you can use the key-presses to trigger the corresponding animations on a separate Sprite (pinned on the one that has the Platform behavior-the box).
Now (finally), for ducking and sliding.
Ducking should just trigger an animation and perhaps decrease the height of the Sprite that hold the collisions for your character (the one I was referring to as box).
Sliding is a bit more involved. You could emulate it with the following events, including a boolean variable and the timer behavior:
When Down key is pressed----> set Boolean "Sliding" to True , set timer "Slide" to 1 second
If boolean Is Sliding----->Platform, Simulate movement Right (for example), set Platform max speed to 600 (for a fast dodge)
On timer "Slide"----> set set Boolean "Sliding" to False...
I hope I was helpful and sorry for the long post... X)