Sideboard Erebos, God of the Dead and Dark Betrayal if you're concerned about Siege Rhino.

I like this list.

Wondering if Agent of the Fates is better than Mogis's Marauder and Master of the Feast. Does it test well?

If you do decide to include another BB creature, consider Nykthos, Shrine to Nyx. It'll help get your creatures bestowed quickly.

Ok, so, I'll try to keep my suggestions on the budget side of life as i see you've intentionally left out all and any fetch lands Polluted Delta - and Thoughtseize .

That said, your main board has problems. Spiteful Returned has to go. Period. Replacing it with 25cent Gray Merchant of Asphodel is a great idea. Especially to deal with Siege Rhino. 2x Empty the Pits is way overboard. Only 1x if you deem it a necessary win con but you're losing 50cent Murderous Cut as a delve option and amazing control card. You could even drop one for a second 5$ Whip of Erebos. Then Pain Seer, I just don't like it. It's dangerous with the higher CMC cards I'm recommending, but even if you don't take my word on those, I'd still say Sign in Blood is a way better 2 drop for digging cards out and it feeds delve cards faster.

Sideboard problem - Crippling Blight It overlaps with the useful intimidate option on Mogis's Marauder and it overlaps with the hasty response to red decks in Pharika's Cure. I'd drop all 4 Crippling Blight for 1x Whip of Erebos 1x Pharika's Cure 1x Dark Betrayal and 1x Drown in Sorrow

Thanks for the comments, guys!

Roccovsky- I've added an Erebos to the sideboard, and will probably be adding Dark Betrayal soon. The problems I've encountered with Master of the Feast is this deck punishes bad hands and bad plays with aggression, and the Master removes that advantage. Mogis's Marauder is good except against black, and I can't afford having a 2/2 for 3 against the Abzan and GB decks.

VOLTAFISCHER - I am looking more towards budget, but if I can acquire the cards, I'll definitely run them. I made a lot of edits. Spiteful Returned has been incredibly good in playtesting, and bestowing him is very relevant. Empty the Pits is getting moved to the sideboard, and I did encounter that problem with Crippling Blight. It will be replaced soon.

So I looked over it and recommend that you add at least 3 Master of the Feast. I think the Spiteful Returned isn't really doing much for the deck. Also get rid of the Grim Haruspex. Finally, you might want to consider Gurmag Swiftwing. I know that he isn't that strong but, he has haste and I think that is more relevant in your deck. I would also mainboard the Mogis's Marauder again. It shuts down so much and yes Siege Rhino can block it but, Sylvan Caryatid can't and neither can Courser of Kruphix and I think those are what gives you trouble. Asphyxiate is also a poor man's Hero's Downfall.

I've been testing Master of the Feast for the last few weeks, and he's actually just bad. Aggressive decks take advantage of your opponent 1.Keeping bad hands or mulliganing and 2. not being able to answer all of your threats. Master completely eliminates that advantage when you're ahead, and loses the game when you're behind. Spiteful Returned has been excellent in testing so far, better than most options. In one attack, it's guaranteed to do as much damage as Gurmag Swiftwing does in two attacks, and he's a much better topdeck than Swiftwing. Grim Haruspex will probably be moved to sideboard for removal-heavy matchups, and some of the Mogis's Marauders will likely move into the mainboard. I own the playset of Hero's Downfall, and will probably move more into the sideboard.