I got this information from another player: here's how to win level. try and make a hole in the middle without unlocking the chains. then you can unlock first one side, burst the bubbles above the black bubbles and then do the other side. it will take a few tries, but that's the best way. the lava bubbles (black) activate when you unlock the chains. and with every bubble used they start melting. you don't have to hit them to activate. just don't break both sides of the chain at the same time or the sludge will get you.
I am not playing this game so I am not sure. I will see if I can get some information.