One of the first things we saw when Death Knight was first revealed, was (predictably), the Ghoul Charge Hero Power. It summons a 1/1 Ghoul with Charge that dies at the end of the turn.

But we didn't know what the upgraded Hero Power was, and there were a few possible interpretations as to what it could've been. Celestalon has confirmed on Twitter and it summons a 2/1 Ghoul instead of a 1/1 Ghoul. The choice of a single 2/1 Ghoul as opposed to two 1/1 Ghouls is likely to prevent the counter of Corpses from scaling too quickly that could otherwise happen with an extra Ghoul.

Quote From Celestalon
2/1 instead of 1/1!

Currently in the game, we only have 3 cards that let us do this: Justicar Trueheart, Baku the Mooneater, and Sir Finley of the Sands. This means that for the time being, this upgraded Hero Power will only be accessible in Wild, but we're sure to see some more cards with this ability at some point in the game's lifespan.

Justicar Trueheart Card ImageBaku the Mooneater Card ImageSir Finley of the Sands Card Image