Had to do other things before going back to this effect, but now I’m on it
Here is a little update of what I added :
PopcornFX :
Shimney smoke.
Rails shards.
Portal mesh & effect + calculation of the distance between the portal’s position and the train’s position.
Morph (logo & plexus).
UE4 :
Imported the effect from PopcornFX.
Created a dissolve material function.
Used the previous material function to create a simple dissolve material.
Modified the PopcornFX material of the train with the dissolve material (The dissolve is done based of the result of the distance calculation previously done in PopcornFX).