I played against Death Knight as mage multiple times but whenever i had a water elemental at the board(cause of the card Tsunami) and the enemy Deathknight was using " Threads of Despair " ( 2 mana shadow spell ) the moment an elemental of mine died all the other creeps in the board were frozen. That made me lose twice in previous month and just happened to me today before 5’ again. The spell says: Give all minions " Deathrattle : Deal 1 damage to all minions. " It doesn’t say the enemy elementals hit their other friendly minions with their attacks! DK can annihiliate all mages in this expansion cause of that. This destroys all the fun of playing mage.
Water Elemental freezes any character it damages, and that includes damage by deathrattle. This isn’t a bug
Just an FYI with threads; A life steal minion will heal for each target that takes damage from the deathrattle and a poisonous will kill the whole board