[Christian Mejia]

I suposse that the easiest way to achieve this effect is by using Time Remap.
After you add the Particle Playground effect, Pre-compose that layer (CTRL+Shift+C) and then Right-Click the pre-comp then go to “time” and finally “Enable Time Remap”
Two keyframes will be created, one at the start and a second one at the end. In the timeline go to the part where you want the particles to freeze and add a keyframe. Then copy that keyframe and paste it where you want the animation to continue. Then you just have to play a little with the position to move the the layer where you wish.

Hope It Helps.

[Christian Mejia]

Well, actually to work with poorly blue/green screen is almost impossible…I mean, it’s very hard to achieve good results.
Anyway, you could try to apply several times the Color Key Effect to be sure to hide all the different shades of blue….maybe 6 or 7 times….then use the Simple Choker effect to have a better shape of the footage and then try applying the keylight.

[Christian Mejia]

You can use Sony Vegas or other Video Editing Program to break the video…If you want to do it in After Effects you have to hit CTRL + Shift + D in the timeline exactly where you want to break your video to literally Trim it.

Hope It Helps…Good Luck!