The effect on Baleful Banker isn't anything new, but the fact that it's a neutral card makes it instantly very exciting. We've seen a similar card in Mage, but now you can play this in any deck you want.
So let's start with Warlock and all of its demon synergies, including the infamous Voidlord. Then, let's look at Rogue and Fal'dorei Strider, which can keep putting those spiders in your deck.
But the best one yet comes from Shaman and the new legendary Shudderwock that repeats all the battlecries, and will keep doing so with the help of Baleful Banker. So all in all, this is one minion that you can combo out really well with!