New endgame content

Original game is known to have sort of disappointing ending: there's nothing else to go, you are just stuck at certain points of the last level.

We can make better.

@sotiredofyours, @gsomix, any ideas? What could we make?

I am thinking of a boss battle (with "the boss" being a bigger and maybe handmade animated sprite that may swim and throw bombs at you, with a lot of HP and custom behavior).

Any other ideas (like a puzzle stage or somewhat more explorative ending, like a portal to another world or something) are also very appreciated.