Hissing Heart

Hissing Heart is the most annoying of the five bosses and sucks

You will have to fight it at the end of world 3, Inner Oasis, after beating levels 41-59, in order to continue to the following world.

Fight
You spawn on a battlefield filling one screen and your objective is to make Hissing Heart hit itself. The stage will get smaller after every phase, be careful!

The boss fight has three phases:

Phase 1
After spawning, depending on which side of the screen you are standing right now, it will try to sweep you away with one of its hands, just dodge it by running away. After that it will try to crush you, dodge the hand and jump on it, be careful not to touch the acid. Just jump on the green platform next to you and it will hit itself when trying to crush you if you jump over it or morph through the platform.

Phase 2
Hissing Heart will now cause some blocks to fall down and then take a sweep again - avoid it at all costs. Again, it will try to crush you, dodge its hand, jump on it and get on the green platform. Make it hit itself and get down.

Phase 3
This is the final phase, almost done! Hissing Heart will again take a sweep after trying to crush you with some block. Dodge the enemy and make it hit itself again. Great!

Room
The boss fight happens in a closed room, the floor is made of blocks now, but it will get smaller. The walls are no exit either, the ceiling is just some intestines, similar to Intestinal Ire.

There are two platforms at its head (?) and he has two big hands with which he will attack you.

Secret tip: Use a light character like Kawaii-San to jump over its fist after it attacking itself and just get on the platform again! It might take a while to get it done consistently, but you will be able to beat the boss in record time when using this strategy!