I am tempted to record a video where I go full munchkin with a green mono-color build, and upload it such that you can see it. And try to defeat every enemy I find. I have defeated the Chieftain a number of times with a green mono-color build - green can even get good direct damage, with for instance the heart symbol.
I tried it some more, and poison is useful in several cases. It is especially useful at the very start, since you have a large mixture of colors of symbols and only one dual color symbol, and dealing damage consistently can be difficult. But if you get off a bit of poison, time may be on your side, even if you never hit a damage dealing effect again. That can give you symbols and tokens to get rid of some of the colors, and even removing one, and especially two, can make a deck much more powerful.