So the theory is (I don't have the quest to try this out) witching hour and the marsh drake give early 5 attack summons to complete the quest, and Splintergraft can turn anything into a 10/10 and it will cost 0 allowing for some serious combos.
If you bounce Splintergraft back to you hand you can play him for free again, and get 2 10/10s for free. If you have Ixlid, Fungal Lord and a charge minion, that can be 4 10/10s with charge, but this is pretty insane without all the cards needed for the OTK play. Free echo cards also means 7 10/10s so theres that too. Copying Ixlid has proven to be pretty nuts. People have come up with some pretty cool OTK decks using Ixlid, Splintergraft, and Faceless Manipulator already.
Basically, a whole lot of large minions aren't super necessary now to make this quest work. We can generate some, and copy others.
If you think this deck sucks, at least you know what I'm aiming for, because its seems crazy if you can pull it off. I don't know if this will work since it doesn't really start until turn 3 and might not have enough taunts or sustain to last.