Kill orange then red spawn, and stick to the top of the chamber. Monsters can still spawn in the bottom island if you’re not high enough.
Kill the red spawn, and head to the exit if no orange spawned. Stay near the exit, the last wave can still spawn around the orange location.
B_Combat03 – left entrance
Head toward the red spawn on the right, then to the top one. Check if an orange spawned. Stay at the top.
B_Combat03 – right entrance
Head to the red spawn, stay there.
Kill the red spawn. If no other monsters spawn, head to the orange and stick to the top of the chamber. Otherwise, stay in the red circle, kill any enemy at the bottom of the stairs, then go up.
Check the orange spawn and head to the red one. Stay at the top.
Kill the red spawn. The next spawn will usually be at the top. If it spawn in the center, some monsters may also spawn in the bottom.
Kill the red spawn. The next wave will usually be in the top right island. Go there, and stick to the top-left.
Every monsters will spawn around the red area, so stay there.
B_Combat21 – left entrance
Check the middle red spawn, then the left one. Stay on the left side.
B_Combat21 – right entrance
Head to the top right spawn, then the center. Stay there
A couple monsters will often spawn in the rightmost island. Check the center spawn first, then head there if no other monsters spawned.