riftbreaker brutal 500% survival tutorial, on metallic biome

As the majority creatures in metallic biome are weak to acid and the rich natural resource, in lower difficulty this biome is somehow drone-tower-spammable, and it can be quite easy.
However when high volumn of monsters are added to the wave, some strategies do prove to be more reasonable here. The central point may be the use of walls, which is far less important in all other biomes.
Subtitle added so that the watchers should be able to understand what was going on.