Compositing/render question

Hey,

Im working on an project in which i modeled a stargate and a jumper (spaceship from stargate). I also have some video footage in which i want to place my models. The tracking and camera resolving is done.

Now i have on the one side the problem, that i want some tears/scratches on the ground where the stargate is grounded in (i tried a uv map on the ground (background layer) and created there one with some scratches but in the result there is nothing rendered) - so i tried it with a plane in the foreground cause i thought if the uv map is transparent except of the scratches… doesnt worked as well. so how i realise this? it should look like (https://youtu.be/CVPcT0dJmoY?t=2946 ) but he uses blender renderer and i use the cycle renderer

the other problem is, that the spaceship should come out of the stargate - so it is animated but should “appear” (like that https://youtu.be/tNSiS9wN-GI ) the problem is, that i dont know if i can use this. may you guys have an other idea.