
Hollow One can be played for free from hand once we have a Phantasmagorian to allow us to discard three cards, which, along with a free creature like Memnite or ,] triggers our Vengevines to come back from the graveyard and also triggers our Prized Amalgams to come back at the end of turn.
Sometimes, we can keep an opening hand that has no dredger but has a Phantasmagorian, but this usually involves either multiple Hollow Ones or multiple Vengevines along with at least two free creatures to get the Vengevines into play from our graveyard. Even before Once Upon a Time was banned, we wanted more dredge creatures, and now that it is no longer legal, going up to four copies of Golgari Thug is a really easy choice to help ensure we have a dredger in our opening seven as often as possible.

The problem is that we also can't really mulligan with the deck (unless we have Serum Powder) since every mulligan we take puts us another turn away from discarding to hand size, which is our only way to start dredging and filling our graveyard). Basically, for a hand to be keepable, we need a dredge card (either Stinkweed Imp or Golgari Thug) or maybe Phantasmagorian, depending on what the rest of our hand looks like.

The good news is that Once Upon a Time isn't actually very good or necessary in the deck. Yes, the build of Manaless Dredge we played for our videos had Once Upon a Time.
