I don't like the card.
If you kill a creature, it prevents the creature from being played for four turns.
This is OP if you look at it from a similar standpoint that I looked at it from: the enemy.
I have a 
rush deck using phoenix's. I play one phoenix and then you play that undead knight. All of a sudden, I have an ash on my field and whenever I try to play a phoenix, I get an annoying card text that says "This creature can't be played for four turns."
This is overpowered. If not, then compare it to silence. Silence costs three quanta and prevents any card from being played for one turn. Your skill costs two quanta and prevents a certain creature, usually the main creature with the current meta-game, from being summoned for four turns. Four turns is all that is needed to start and end a game, as demonstrated by three turn kill decks. Four turns is all that is needed for the opponent to summon enough creatures to either win the match or guarantee the win of the match. Four turns is a long amount of time, which is why Congeal and Basilisk Blood are so powerful. Even Freeze is very powerful.
I would nerf this to one or possibly two turns. One turn means that if the creature dies, the creature can't be re-summoned next turn. Two turns could be overpowered.
You talk about how powerful Congeal is, while forgetting to mention why this card can't be on the same tier as Congeal. The 6
cost warrants having a 3|3 body in addition to the reusable ability in my opinion. Decks are often centered around getting out one creature, but not always. And I am of the belief that the opponent can still work toward removing this card before it causes too much damage. Consider the fact that it ONLY deals 2 damage with its 2
costing ability. The odds it'll kill a "boss monster" grows astronomically low with Death's current slow CC.
