“We want cards to work the way that you guess they might—in other words, we want the game to work intuitively,” the team wrote. “So we want to be extra clear that this update isn’t a change in depth; instead, it’s one step in an ongoing effort improve Hearthstone’s mechanics.”
The two changes are that minions with the “after” keyword will only activate their effect if they’re in play at the time and in-play effects will no longer trigger in-hand effects. Confused? Gameplay Engineer Josh Durica walks you through these changes with in-game examples below.
Source: YouTube