It would be great in control decks with Sylv... better than Syl+Shadowflame in a lot of cases
Edit:
It might even see a lot of play without Sylv..
Priest is obvious because of their quest, but I think it has the least chance here actually
Hunter also has a 1 mana deathrattle minion coming out, and they have Grandmother / Highmane / wolves / rat pack / etc. Also Hunter are getting the "Trigger a friendly Deathrattle" on a 3 cost card now, so Deathrattle Hunter is making a lot of sense and this card seems strongest here simply because the Deathrattles typically add to your board, whereas Priest will generate more resources to hand.
Some edge cases could be:
Jade Rogue. I've been playing Dog's Jade Rogue deck which is fun as hell and actually decent. I can easily see this card fitting in to generate more Jades from Swarmers.
And then you have the greedy N'zoth meme decks that I've tried in the past such as:
N'Zoth Shaman: Triggering White Eyes/Aya/Cairne without worry of a Hex/Poly is awesome!
N'Zoth Mage: Mage Legendary will be fun as hell but also the more obscure Twilight Summoner makes even more sense. 8 mana for a 1/1, 5/5, & 3/4. Sweet!
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Not to mention you can combo this with
Hoarder / Mistress / Thalnos for emergency draws or healing
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So yea I think this card will be tried.