Thank you for the feedback! The difficulty scaling took a bit of time to implement and I wasn't sure how many object patterns I needed to make to keep the game loop from getting stale, but in the end it turned out pretty alright. For context, both rings and rocks are classified as objects and they follow a spawning system in which pre-made patterns are randomly selected and spawned one at a time (though, at high speeds, patterns may spawn on top of each other--unintentionally). As soon as the last object in a pattern reaches a certain point, the next pattern is spawned. In retrospect I realized I never used any red rings for any patterns, so there's only 4 ring colors that appear instead of the 5 that were made...whoops!
As for the rival/boss fight, I mentioned in another comment that there were originally 3 rivals planned, but we were only able to add one due to time constraints. I wanted to add at least one rival to the game since the premise of the game was designed around a Surfball tournament. Had the other 2 rivals been complete, there would have been a ranking system (4th to 1st, rank up for every rival defeated) and that would result in earning more points from rings and drones--basically a point multiplier.
For the art style, I was aiming for a simple, stylized vibe to enhance the arcade-y nature of the game (I used 480x270 as a base resolution). Details such as different drone designs and the player wobble animation were fun to make as well. I'm glad you enjoyed it!
And yes, it is super satisfying to hit them drones with the ball! (BONK)