Question: btd5 how to beat fast upgrades?
Answer: Buy 2 Glue Gunners at the front. Pop the reds with spikes (optional if you want NLL).
Buy a Monkey Ace (anywhere) during Round 3 and get it 0/2. It will be upgraded 0/3 at the end of the round.
Buy 2 more 0/3 Aces during Round 4. ... 
Start Round 5 and wait till all BFBs are on screen.