This event is pathetically easy to code for.

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Heres what you need to make.
-Rain Drops
-Snow Flakes
-Splashes
-Ground Snow

Note: Make splashes dissapear quickly to keep your games speed up. So make their animation loop 5 times and animate at speed 100.
Make ground snow stay on the ground and destroy it when the player steps on it. Make it bouncing ball with a down direction but make it stop when it hits the background.

Thats all!

Heres what you need to do to them.

-Make the rain and snow bouncing ball objects, take out all of their deceleration, randomizer and security. Set their initial direction to down. If you have a big level make sure they dont follow the playfeild.

Heres the event.

Rain drop/ snow flake leaves the play area at the bottom- Wrap Around Play Area.

For a splash. Same thing for ground snow.
Rain Drop collides with backdrop or any other object-create splash at (0,0) from rain drop.

Very Easy to do.
Hit me up at mttgles2003@lycos.com