Great deck! just a couple suggestions. I would drop both Syncopate for Negate since the only creature that could get in the way would be Ravenous Chupacabra, since all of your creatures will be unblockable mostly. I would also consider putting in Fatal Push instead of Vraska's Contempt because on turn four, you will want to be playing two Rat Colony so fatal push would be better since it's cheaper. Between Unwind and Negate, I would choose negate since it's cheaper and there's not much else you can play instant speed. Great deck though, I'm gonna take it and budgetize it and maybe order it.

SchleyGuy, thanks for the feedback. Since beginning play testing, I had already bumped Negate up to a playset. It came in pretty useful. I'm gonna have to find my copies of Fatal Push. Still needs more testing overall, but it seems pretty fun. There's been a few times where I get 4 rats and then the next turn Tetsuko Umezawa, Fugitive hits the field and boom, 20 unblockable damage for the win. I've been considering switching in Mastermind's Acquisition to find Tetsuko quicker instead of some of the general draw cards.

AnderDan, your welcome. I am putting together my own budget U/B rat colony deck, and have run into the same problem as you with getting Tetsuko Umezawa, Fugitive out. I decided to run Razaketh's Rite instead of Mastermind's Acquisition since it has cycling, so you can cycle it away if you already have tetsuko in hand. I also want to find a way to get more black mana without running expensive nonbasics, since Bontu's Monument makes all the rats cost . I am also debating cutting Secrets of the Golden City since it has  in it's mana cost, but i'm not sure. My deck is linked here, if you want to check it out. U/B standard rat colony

Bontu's Monument should allow you to cast all these rats cheaply, while draining the opponent.

Archfiend of Ifnir would allow you to place out a lot of -1/-1 counters when you discard your cards.

Faith of the Devoted allows you, for a small additional mana investment to drain your opponents, when you discard your cards.

Merciless Javelineer allows you to place out more -1/-1 counters.

Ruthless Sniper does the same, for a small additional mana cost.

Tomb Robber grows bigger, permanently, and provides potential mana fixing.

Fateful Showdown deals a *lot* of damage.

Hazoret the Fervent deals damage for a small mana investment.