The idea of the dirt mound was to have a tsunami of rock/dirt formed from the beam's pressure destroying the town. The initial technical challenge was to simply get the volume of debri needed to achieve this effect. I tried to use rigid bodies at first but as suspected there were just too many object to sim . So that leaves instanced particles combined with fluids. Thankfully nParticles supports self collisions so the workflow was pretty straight forward. I used a plane and emitted on the x-axis, a second plane was then used as a passive collider to push along the debri. Then with some expression writing I added faux rotations and came up with this.
The sim was getting too heavy with all of the instances and the interparticle collisions. So I scripted a killfield which culls the excess as it moves forward. I then added the fluid container to fill in the gaps from the instances to give it a fuller appearances. I added a few debri splashes against the buildings to help convey the fluid like nature of the debri mound.
The idea for the bus crash was that the wind generated from the beam causes the bus to go tumbling into the church. The bus itself was hand animated. The first thing I did was cause the bus to dynamically dent upon impacts with the ground and the church. I did this by turning the bus into an nCloth object. The second effect was to emit debri particles from the ground upon contact. This was done by assigning toon outlines to the bus and then using the outlines as particle emitters. I then blew out the windows on the bus upon impact with the church using PDI.
It's pretty well known that Maya's rigid bodies are useless, so we knew right from the start that we would have to figure something else out. After some testing we decided to go with PDI. I set up a brick wall that had already been modeled, at first I just had the bus knocking down the brick wall but the end result looks very generic and fake. So I used PDI's fracturing and clustering features to break up the uniformity of the wall destruction. PDI enabled me to itterate extremely fast so getting the desired look was relatively painless.