Video: The folks over at HearthSim came up with a way to bypass the 10-card hand limit in Hearthstone, and eventually end up holding 12 cards. In Hearthstone players can only play cards from their deck that are currently in their hands. And the limit of that is 10 cards. Attempting to add a card from the deck to the hand when it's already full would discard that additional card.
But it looks like there are exceptions. It requires casting Shadow Madness on our minions and triggering a whole bunch of events with specific cards before that spell takes effect. YouTuber Disguised Toast made a breakdown video of how it works exactly.
Theoretically, the upper limit could be even more than 12 with this technique, depending on the number of Shadow Madness cards. But that would be extremely hard to trigger. Even this needs a ton of luck.
This might get fixed soon, as other tiny exploits have been before, so better have fun with it while you can.