It seems 6 mean MAXIMUM 6 zombies exploded. When you max your Damballa, it means 15 maximum zombies exploded. The fact is each explode uses maximum 3 zombies, so it means the Damballa core can explode up to 5 times (i’m not sure about that, but you can test it when you play versus many mobs like Uphill defend, it blows many times and I dont have time to count it). Damballa damage and aoe is very huge, so just MAX it and enjoy the damage.
I tested low level damballa before, and it is very weak. Max Damballa is a MUST.
Today, I went solo Uphill. And i reached stage 27. Hope IMC will give skill reset at the end of this event, I can reset my skill to optimize the damage and i think i can clear uphill by myself. When i clear it, i will post the picture