If Wilfred Fizzlebang is played while Lord Jaraxxus is on the battlefield, the two will have a special interaction, referencing their interactions in World of Warcraft.
When a Cobalt Guardian is killed, it will say "ERROR 37". This is the error code that players received when attempting to play Diablo III during its initial launch.
The Flying Machine card says "They came from behind" when killed, a reference to the same line said by Gold Five "Pops" in Star Wars Episode IV: A New Hope and Warcraft 3, where the flying machine also says this line.

The uncollectable card "I Am Murloc" displays a murloc clad in armor which holds characters reminiscent of Spongebob Squarepants, Patrick Star, and Mr. Krabs from Spongebob Squarepants.
The card description for Fel Reaver, "So reaver. Much fel. Wow." is a reference to the Doge meme.
The card "Mana Wyrm" appears to have taken its art either from World of Warcraft Burning Crusade's Cinematic trailer, or was directly inspired by it.
Some of the songs played during the matchmaking process come from Warcraft 2: Tides of Darkness.
The card "Power Overwhelming" is most likely a reference to StarCraft, where the phrase appears both as Protoss Archon dialogue and a cheat code to activate god mode in the game.