Tips for Farming Yellow coins
I’d advise playing one of the earliest arenas on the hardest difficulty.
You don’t get them all the time, but you can either earn them as rewards for clearing all the waves, or destroying a Token bot that can sometimes appear.
It’s a bit of a grind, but it’s worth it.
Note: Discovered the token bot! Grab a saw and try Pit Stop on hard. With a charge attack you can really quickly take out zombies. The cult leader dressed in white really makes trouble however.