Just nerf the quest. Why do you let summon Tamsin so soon?. Why all the self damage spells and cards like Crystallizer cost 0-1-2?
Just boost the mana cost of all the cards of the strat. They are unkillable. All warlocks in Wild are demon seeders. Just stop being hilarious and nerf this non sense overpowered strat already Blizzard HS devs. Are you being serious?. Why are you waiting for?.-
Nerfing is kinda like vengeance. Maybe someday in the distant future everyone who has wronged you will be dead, and in that you could take some cold comfort, but your crappy deck will never be good
I like Demon Seed.
I can play Pit Lord. I can play Ancient Shade. I can play Hakkar. Without downside. 
Demon Seed seems like a nerf target but I did beat one with DR Hunter. And then one with Spell Damage Mage (Mozaki + Coin + 4 Arcane Bolts).
All they really do is damage themselves so if you have a board presence or direct damage, you should do ok.
You have to realize that damaging the hero you play is part of warlock’s strategy regardless of whether or not the quest is being played. Self damage cards and hero power existed before and after Demon Seed in both Standard and Wild, and are still being made. It is pointless to nerf every card that can contribute to Demon Seed. The only way to nerf it without punishing other warlock decks is to target Demon Seed or Tamsin reward card itself. And the quest has already been nerfed once.
I wish we got SI:7 and combo support every expansion and miniset like warlock gets demon seed support
That is why the quest itself is all that needs to be nerfed. If we had a “discarding now returns discards to hand” quest (for 40 damage soulfire turn 10, for instance) we wouldn’t say nerf soulfire, we would say nerf the thing that breaks soulfire.
Because it is quite easy to beat
How can I beat it with my deck?
What card do I need in my deck?