Here's my favorite gem (Though more narrow than you might be looking for):
Zombies Drafter: Come on. Throw it back at me. I dare you.
Maybe it's not so bad at 360, but I've always wanted more discard available for black, since it's the color's main form of interaction other than removal.
You were looking at ways to tie your blue section to the sacrifice/pod themes, so I suggest lots of clones: the interaction with undying/persist creatures is second to none, and they also help you jump up the pod chain (Though only if such a creature is already in play)
I'm currently testing
Wakedancer as a pod/zombies card (But sadly I haven't gotten any games in with it yet)
Depending on how amenable you are to proxies, Shadowborn Demon looks promising, from the M14 spoiler.
Oversold Cemetery is usually worth testing in such a graveyard centric enviornment
Krenko, Mob Boss is a card that has been preforming admirably for me: Feeding Eldrazi Monument, Providing Red decks with inevitability, and being generally a better curve topper than I expected him to. Shoutout to Kranny for the suggestion on him.
Pyreheart Wolf performed well for me before I added the pods, he's been excellent afterwards.
The red deck might not really need the help but,
Brimstone Volley. My god.
Lastly, While I recognize that your multicolor sections are REALLY right (3 cards each, how do you live?!?!?),
Voice of Resurgence seems like it would perform well.