He sends a massive wave of mostly anything monsters (like Fangs) along a broad front to test bases with good tower coverage but many exposed decoy buildings. Kozu tribe can be killed if you find all the booby tarps with monsters like Bolt. Then, you can practically march in with stronger monsters and kill everything since its defense towers are not storng but the defense towers are covered with blocks and booby traps.
For map room lvl 2, you can get about 6,000,000+ twigs, 5,000,000+ pebbles, 5,000,000+ putty and 2,500,000+ goo if you fully destroy a lvl 42 yard.
There are many ways to farm kozus, the most efficent way is this method
Here is the Yard Planner of the Kozu tribe
Now here is the kozu tribe with the tower ranges