Brainy Beat

Brainy Beat is the second of the five bosses of Slime-san's maingame. It seems like a worms brain is at its butt? I'm too lazy to check that.

You will have to fight it at the end of world 2, Organ City, after beating levels 21-39, in order to continue to the following world.

Fight
You spawn on a rather long road facing Brainy Beat as its hanging from the ceiling? It looks similar to a certain wall made of flesh.

The boss fight as well has three phases:

Phase 1
You will have to avoid its laser cannons through most of the battle. After some time he will call for help and a few wormies will appear. Just use them to get up to that button at the top, a cannon will shoot some acid at Brainy Beat.

Don't be too slow now, it will try to get away, follow it!

Phase 2
Again, avoid its laser cannons and when it calls for help, use the wormies to shoot that cannon once again.

It will try to get away a second time, just be sure not to get caught up by its obstacles.

Phase 3
This is the final phase, almost done! Brainy Beat will try to hit you once again with its laser cannons, just dodge the lasers a third time, use the next wave of wormies to shoot the cannon one last time. Epic.

Room
The boss fight happens in the city, probably on an empty street. The sides are blocked by his brainy walls.

Secret tip: You can just stand below the button platform as the laser cannons won't reach that place. Just make sure to dodge incoming wormies.