Get something to occure when its "on-screen"?

I have things that i want to only take place when the player reaches it, to be more specific, other scrolling platforms i want them to idle or not exist until the player reaches their location.

Size and Position:

Is Object On-Screen?

If yes, Action.

Thanks! If i knew how to thank you for the post, i would. lol :P

Looks like you just did, ha ha.