The next update for Hearthstone and the developers are changing 3 cards in particular. Manawym, Aviana and the giggling inventor are weakened somewhat by increased mana costs.
Here are the official explanations and the reasons for the individual adjustments:
Hearthstone - giggling inventor
“Giggling Inventor is one of the most powerful and popular cards we've ever published. There are few disadvantages to it, and as a neutral servant, it is played in almost every deck. We believe it is important to take risks when developing powerful maps. Especially neutral servants with mockery encourage interactions between servants and make games more interesting. However, Giggling Inventor has outgrown her intended role a little. It shouldn't be quite as efficient as it is right now.
We originally tested this card both in the current standard format and with upcoming cards as a servant for 6 mana. Ultimately, we found that it was still too powerful for a neutral card without special requirements. For 7 mana, Giggling Inventor will probably find space in fewer decks in general - and be much weaker especially for quest villains - but it will still be playable for certain deck types such as evolution shamans under certain circumstances. "
Hearthstone Mana Wyrm
“Over time we have moved away from overly powerful 1 mana servants like mana wyrm. Manawyrm can often decide a game if it can be played on the first turn and cannot be eliminated by the opponent. In addition, he stopped us from developing powerful and inexpensive mage spells. Manawyrm should remain an option for decks that were built around the map, but no longer pose a huge threat on the first turn.
For 2 mana, it is easier to destroy on the same turn as it is played. It is also more difficult to empower him with cheap spells at the start of a game. We expect it will continue to be played on decks with lots of cheap spells, but it should be less attractive to other mage decks in the future. "
Hearthstone - Aviana
“By increasing the cost of Aviana to 10 mana, it can no longer be played on the same turn as Kun the Forgotten King without the support of cards such as Stimulate or The Coin. In addition, Aviana can no longer use Psychedelic Melon and Pull kun. This makes the combination of Aviana and Kun a little less reliable, but at the same time players who love these types of decks can still play them. "