- Ally AI robots that require your own upgrades to become a better robot (chapter 3)

- tiered elements (fire > magmatic > volcanic) (repeating challenges at a higher difficulty)

- shielded enemies that can only be hit on the back (chapter 3)

- enemies that can't be attacked on certain limbs with a glowing aura (1 at a time)

- switches that can be operated by player or operator-bots

- operator-bots wont attack, but instead operate the nearest switch in the battlefield

- elements: shadow > blink > umbra (can physically go through enemies, and enemies cant hit you, but can instead hit others beside you), acid > toxic > nuclear (works like fire, but slows enemies down and it cant completely kill enemies)

Neat ideas!

I like the idea of enemies that can only be hit in the back. Maybe an interesting variant is just something that can't easily be hit from the sides.