A cavalry of noble knights, powerful steeds, and potent spells is coming to Hearthstone with The Grand Tournament, the second expansion to the card game. It introduces a new card type called inspire that triggers after you use your hero power and affects all friendly minions with the Inspire keyword on them.
A number of cards with the Inspire effect have already been released. Some of them are quite good, while others aren't as impressive. The Grand Tournament also introduces a new way to protect inspire minions that you want to have on the board for a while, letting you summon taunt or Divine Shield creatures over them.
There are a lot of cards that can make the Inspire mechanic really fun, including Thunder Bluff Valiant and Confessor Paletress. Both of these cards have high health making them less risky to play on curve and the ability on Confessor Paletress is pretty solid too, allowing you to get some nice value if it sticks around for a few turns.
Other cards like Maiden of the Lake and Coldarra Drake are a little bit underwhelming though. Their effects are pretty small compared to the cost of using your hero power. And they require you to keep a minion on the board with them for multiple turns, which isn't always an easy feat in hearthstone.