I have been thinking about ways to improve this after the jam:

• Add a active block mechanic: before getting hit by the boss, show a quick time event, slowing time and allowing the player to press a button to block the attack, show a progress bar with the time remaining, the time to block the attack reduces with higher levels. Sparks, sound effect and knock the boss back when successfully blocked.
• Maybe add i-frames and make the dash more sudden... ?
• It would be better with unique bosses, at least different colors/sizes and perhaps unique patterns of animations, or special animations unique to each boss/month. The random animation pattern offers variety, but it doesn't offer anything for the player to learn and overcome. it could be seeded so re fighting the same month/year has the same set of animations. Also I think there should be animations with special movement like charge forward, to the side, jump up then land on the player ;)