Two stars
All four potions
Clear the bubbles under the chain as quickly as possible. (You can safely shoot the linked bubbles as long as you haven’t broken the chain.) Unlock the chain.
Clear the bubbles up to the row of pairs of black bubbles AND between the black bubbles. (Don’t shoot linked bubbles yet.)
Then plan your shots according to the bubbles coming from the cauldron.
For instance, if the two bubbles in the cauldron are yellow and then green, use the yellow bubble to shoot the link and the green bubble to clear the cluster of green bubbles on the ceiling.
That will clear TWO sets of links. Clear the next cluster from the ceiling, using a rainbow bubble, if necessary.
All four potions
Clear the bubbles under the chain as quickly as possible. (You can safely shoot the linked bubbles as long as you haven’t broken the chain.) Unlock the chain.
Clear the bubbles up to the row of pairs of black bubbles AND between the black bubbles. (Don’t shoot linked bubbles yet.)
Then plan your shots according to the bubbles coming from the cauldron.
For instance, if the two bubbles in the cauldron are yellow and then green, use the yellow bubble to shoot the link and the green bubble to clear the cluster of green bubbles on the ceiling.
That will clear TWO sets of links. Clear the next cluster from the ceiling, using a rainbow bubble, if necessary.
Plan ahead for each shot this way until 9 holes are clear and you drop the ceiling. It will only take a couple and you have plenty of time before the bombs explode.