Strategy for defeating the final boss

The final boss is the huge goo ball that the player breaks apart in what we'll call phases. It's easier to deal with each phase individually, so try avoiding shooting the boss unless you're ready for the next phase. It's probably the best time to recharge your spit between phases.

During the first three phases, the safest spot to hide is probably the right corner. On the third phase the boss will start to develop black dots. The right corner will no longer be safe after this phase, so migrate to the left side.

The phases will start getting more difficult from here, and you'll have to do more weaving to avoid the boss. It's probably best to strategically start each phase while the boss is bouncing to the right, and then clear the smaller goo balls on the left side.

When the boss has a large black circle, you have arrived at the final phase. There's no need to clear out the rest of the smaller goo, go straight for the kill and you've won the level.

https://www.youtube.com/watch?v=fdibBo5PG9c