Underworld Connections isn't really a good sideboard card. Mainboard or nothing because there aren't really any matchups where it will actually help you. I'd put 1x Sin Collector and 1x Pithing Needle instead. Spark Trooper doesn't seem like a great option here either. While it does gain you some life, it doesn't stick around to help you survive. Personally I would run Blood Baron of Vizkopa over the Trooper if what you want is the life gain. It's also much harder to kill due to protection. Also, you may want to cut a Plains for an Encroaching Wastes to deal with things like Mutavault that can cause issues. Finally, maybe drop 1 Dreadbore for 1 Doom Blade . You may find that having instant speed removal is quite important, especially when you're up against a Gruul bloodrush aggro deck that puts all its resources on one giant creature.

Thanks TheFanatic, I really don't think Mutavault is a big enough deal to sacrifice a colored mana producer, and I do have 6 instant speed removal spells in case it is.

Speaking of which, I do love instant speed removal, and switched a Dreadbore for a Doomblade

In a control deck, I want a body more then a quick life swing so Spark Trooper loses a lot of value if people play around it by leaving first striking blockers back and it also only has a temporary effect while Alms Beast sticks around longer and can start hitting back hard to close the game out.

During testing, Underworld Connections has been a super big part of my matchup versus control, so I don't think I will let it go.

You mention Blood Baron of Vizkopa and protection from black/white's value in the current standard, I agree, and believe it should have a spot mainboard. So I am cutting an Obzedat, Ghost Council

You need a way to draw cards. I tried to build a control deck without draw, sucked big time.

You could employ Staff of Nin for card draw, but unfortunately it is rotating out.