Alright, I'm going to do something new and talk about the changes I made and why.

Marionette Master -> Treasure Dredger:
As cool and synergistic as Mari is, the issue is that her mana cost is far too high in the decks that would want her effect. I'm absolutely down to have Rakdos be a high-mana deck, but I also know that putting in 6 mana to something that barely impacts the board is a tough sell. I'm hoping that TD solves the current issue I'm having with Rakdos, in which there simply are not enough artifacts being generated. My only real concern is that it will undercut the Izzet theme of treasures, but I guess we'll wait and see.

Undead Servant -> Vadmir, New Blood
Putting in a 4-for-1 card into the draft was an interesting experiment, but quite frankly Undead Servant is a bad card. You're only going to be okay with paying the four mana once you already have two in your bin, which isn't always something you can control. The only place I felt okay playing them was a 60-card golgari deck, and that was only to enable Cemetery Tampering. Maybe in the future CT will also bring along some zombies? I don't know. Regardless, Vadmir is a fairly generally good card, and most of the black decks will like having him in.

Prophetic Prism -> Gold Pan
The only real reason Prism was in the cube was the ETB draw a card and leaving behind an artifact to eat. Gold Pan doesn't draw a card, but I think the fact that it comes with an extra mana and is still something that non-sacrificing decks could still use makes me happy with this swap.

Prototype Portal -> Luxurious Locomotive
The portal is a neat card, but considering you're at least 6 or 7 mana in before you actually are copying anything that you care about, I don't think it will be missed.

The Elder Dragon War -> Magda, the Hoardmaster
EDW was a clumsy attempt to integrate the saga theme into red. The issue is that there's already a card that does it better (Fable of the Mirror Breaker). Really I didn't have a ton of problems with EDW, but I think that Magda is a better fit for red.

Yargle and Multani -> Honest Rutstein
This was painful. Removing a giant frog from the list makes me sad, but it needed to happen. I'm hop(p)ing that Bloomburrow adds more frogs that I can justify including, but until that point Rutstein works very well with what you're wanting to do in golgari: bring back big boys and make them cheaper.

Unwind -> Archmage's Charm
I can't 100% call this just an upgrade, because 3 blue pips is very rough. I'm hoping that it presents a challenge for mana construction, and maybe even pushes mono-blue into being playable.

Orim's Chant -> Path to Exile
I frankly thought I already had PtE in the list, and Orim's Chant was at best "cute". If storm or something similar was an archetype in the cube, I'd be more inclined to keep it in, but really it's basically just a fog.