An elite enemy spawns every 3rd wave, a boss every 6th, the bullet powerup every 4th, and the smash powerup every 7th. The total enemy count only increases by 1 every wave which means the normal ones doesn't spawn an extra every 3rd and 6th wave. Made it work by using an array. 

All enemies have their own stats (speed, mass, and strength). The powerups have their own materials, they slowly rotate like in the previous prototype, and they share the same duration. The smash powerup spawns a balloon, lifts the player, then drops with it multiple times while the powerup is active.

Honestly, making the new powerups are harder than the boss battle. All you have to do with the boss battle is put in an array, change the stats, and Instantiate() on waveCount/bossInterval or use "%". The bullet powerup is harder than smash. I just had to learn about 2 new functions for smash while I had to create a seperate object and script for the bullets to make the capsule's top face the enemy and follow them.