Several cards have already made me snicker or even laugh out loud. The voice acting is quite good in Hearthstone imo. Some of my favorites:
Refreshment Vendor
- Funnel cakes! Get your funnel cakes here!
- Grrr, pay up!
- But I have... more... cakes...
Validated Doomsayer
Such a brilliant mean laugh this guy has!
Museum Curator
- DUH-BUH-DUH-DON'T touch that!
Ogre Ninja
- Sneaky! Shush! Quiet!
Cogmaster
- I can fix anything!
- I'll fix YOU!