Book of Spirits - Only works with non-Summoned creatures now. Activation cost raised to 2 mana.
There were two main ways this card was unfair - the infinite advantage it provided with Summoned creatures (e.g. Militia), and the "mana-cheating". In order for the card to be playable, we can't really make it require the full cost of the Spirit creature you are getting from your deck. It was way too cheap at 1 mana, but with a 2 mana activation cost the card is fair for what it does.
So, for some of us it was fun while it lasted, but Guards! Guards! into double Reincarnation Spirit is no more.
======= June Balance Changes =======
This round of balance changes includes only 2 cards - Dark Portal, and Ytix, Realm Guardian - which have been changed for vastly different reasons.
Dark Portal - deals damage to you instead of directly making you lose life.
This change was required because the new Mastery of the Ancients card allows you to get around losing life. After testing it was determined the combination with Dark Portal was too overpowered.
So now, Dark Portal is a combo with Force Field and Unbreakable Spirit instead

Ytix, Realm Guardian - the first power has been redesigned.
The first power of Ytix now reads "Whenever you gain a new hero skill, draw a card."
It is not a secret that Ytix is quite a powerful hero, and we certainly underestimated his mechanics. Both parts of the hero mechanic can be considered too good in certain decks, however we are opting for making gradual changes, because we want to keep the card enjoyable to play.
We added this mechanic to prevent Ytix leading to overly consistent aggro decks, and to encourage the players to use him creatively in decks that can make use of different hero skills shrines. It also has a nice vibe with the hero being colorless, and not having his own hero skill.
We hope you enjoy the changes, and the team wishes you many happy hours with the new cards from Ancients Rising!