AGAINST PRIEST: You need the nuts to win this match-up. Mulligan accordingly by going for Flame Imp, THICC LORD (Vulgar Homunculus). With coin, you might keep Darkshire Councilman to coin out on Turn 2 and dump 1 drops on Turn 3. If your opponent doesn't have Shadow Word: Pain, you should be able to create a HUGE body that should win you the game.
AGAINST HUNTER: You are going to want your beefy early minions to endure the secrets that Spell Hunter plays and for small tokens in Face Hunter as well. Standard mulligans for this match-up of cards like Voidwalker, Argent Squire, and Fire Fly.
AGAINST MAGE: Sometimes it's actually correct to keep onto Soulfire so that they don't run away with the game with an insane Mana Wyrm. This would also lead to Silverware Golem being a potential keep if you're feeling lucky. Make your opponent PJSalt. Otherwise, the mulligan is quite standard.
AGAINST WARLOCK: The key to this match-up is value trading so Boisterous Bard is a legitimate keep given you have your early minions like Fire Fly and Kobold Librarian. Be sure to play around Defile with your beefy minions (if it's control).
AGAINST DRUID: Your only real concerns are for Aggro Druid. Make sure to mulligan for Flame Imp, Vulgar Homunculus, and Dire Wolf Alpha so you control the board early through value trades. Darkshire Councilman is not punishable against Big Druid and Jade Druid so keeping it is fine to create a huge threat.
AGAINST ROGUE: Backstab and SI:7 Agent straight up lose you the game. Mulligan away Flame Imp and strive to make a huge board with minions like Vulgar Homunculus that Rogue can't deal with due to their lack of AOE. Darkshire Councilman is hardly punished if you have coin.
AGAINST SHAMAN: Boisterous Bard, Fire Fly, Malchezaar's Imp, and Voidwalker are super key to sustaining against their early tokens. Soulfire is a legitimate keep as Flametongue Totem can single-handedly turn the game around in the Shaman's favour.
AGAINST PALADIN: You most probably mulligan for a good 1-2-3-4-5 curve, because you don't want to lose tempo or get value traded by Murlocs or small tokens. Haven't played against enough Paladin on ladder so far to give more insightful analysis.
AGAINST WARRIOR: I have played against zero Warriors so far. :P WARRIOR IN 2017 L U L