I tried using 'set move route' but that is making the boulder 'walk' instead of roll.

I want the boulder to roll straight from the top of the screen to the bottom and then disappear and if they hit the player by chance on their way,the game over screen should follow.

I set up a separate event so that when the boulder hits the player,the game over scene should show.but the boulder stops just above the player and nothing happens.please help.

I just tried doing what you wanted to. So, this is how I did it:

Options:
Stepping Animation activated

Priority:
Same as Character(otherwise it'd get on top of it, as a butterfly should, but not a boulder)

Trigger:
Event Touch

Autonomous Movement:
Type: Custom - (Here you'd specify the boulder movement, obviously).

List of Event Commands:
@>Game Over

I think most of these options were obvious, but maybe you commited more than one mistake, or at least you did it different that I'd do it.

Hope it helped.

Hey thanks.I've been able to implement rolling boulders yay! I also created the event that would make the boulder disappear upon reaching the end of the screen.I wasn't aware that the stepping animation would make the motion smoother.

Ok now how do I make that same event repeat for 'n' number of times and then stop?(where 'n' can be any integer)
I mean the boulder should appear,move across the scene, disappear..and then again re-appear from where it had started last time and follow the same process for 4-5 times.

Its interesting, but I've been trying to do the same thing before, and didn't success. Now I did, somehow.

I first placed an event where, when touched, a switch would activate the Boulder event.
Now, for the Boulder:

Autonomous Movement:
Custom:
Move to (certain direction) X times.
Transparent ON
Jump to (where the boulder was first placed)
Transparent OFF
Options:
Repeat Action
Skip If Cannot Move

Priority: Same as Character
Trigger: Event Touch

Events:
@>Game Over

That's, so far, what I did. But if you want it to happen for a certain number of times. Then I'd make an event where, when touched by the boulder X times, the Switch which made the Boulder exists is turned OFF.

Now how to implement the event where the boulder touches X times?I mean how to frame the conditional branch?

I've tried to to it, but I haven't got a clue on how to do it.
I thought it'd be easy, as when using Pascal... or something like that. But I haven't found the way to make it happen.