Boss changes: 

Pyrorb - Max HP decreased from 5000 to 4000, phase transition is less lethal.

Player-2 - Minor graphical fixes, nerfed rapid fire laser attack. 

Stat changes:

Defense is slightly more effective.

Regeneration is paused during the melting debuff.

Base Max HP per level made to scale linearly.

Base defense per level doubled.

Base speed per level doubled.

Base attack speed per level doubled.

I've also started work on the superboss, so stay tuned...