Collectibles: 0 items
In the first phase of the battle you will steer the RoboBun - you can freely move thanks to its boost (point the analog stick in the desired direction and press R1). The task is easy - climb up the walls on the sides and jump off of them into the boss' weak point.  Of course you have to avoid his powerful attack, which fortunately damages only the area beneath him. 
The bubbles/weak points of the enemy can appear on either side.  After landing a few hits, ride down one of the tunnel below (both on the left and on the right). 
In the second phase you have to jump using the launch pads or grab the sponges, continuously being sucked in by the enemy.  At some point a bee will fly up and fire a projectile. The enemy will close its mouth and the platforms will form into a row - get onto Negativitron's s head and hit the weak point (bubble). 
If you find a rhythm, you can in jump along the platform pretty much all the time.  This way you will earn a higher score.  Repeat the process four times.
In the third phase the enemy will be shooting purple projectiles - they're easiest to dodge by just jumping, as the beam will damage you only when touching the ground (explosion). Stick to the middle of the arena and keep jumping across it.  Each series will consists of a couple kinds of attack - the last one will cover the whole width of the stage - just jump up once the beam gets near the ground. 
After a series ended by the wide attack, the enemy will go either to the left or the right - run to the opposite part of the stage.  One of your friends will throw you a cake from behind the wall. Take it and wait for Negativitron to hit the ground. Throw the cake into his weak point (bubble). You will need to jump to hit the target. 
After the throw, run to the other side and repeat the activity.  You don't need to throw down both bubbles - the number of hits counts. In total you will have to ht Negativitron about 4-5 times. In the later part the enemy will increase his speed, but the overall tactic doesn't change - just try to get ahead of his shots.  In the end jump on the bubble placed on the platform.