We dont play Utter End anymore, but sticking Proliferate onto the Golgari equivalent
You want to hinder your opponent and challenge any of the opposing characters using your cards to do that
Being an instant, it also lets you set up key cards right before beginning your turn, including ramp like Sol Ring, shenanigans with Vedalken Orrery, or the ability to attack or tap with an artifact creature on your turn that would normally have to wait through a full turn cycle of summoning sickness
Improvised Arsenal
Due to the nature of color identity, we had not seen a viable option for a morph deck outside of Ixidor, Reality Sculptor, with Animar, Soul of Elements serving as the most practical option at the time
However, Mark is also a fantastic game designer, something that I was able to experience while working with him on the set